Mr Wizards Science 00 in Herb

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Mr. Wizard's

^--'' ', SCIENCE

rjj^, 1SECRETS

By Don Hertier^

/^


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Ben and Sid Ro


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When you buy a book such as this you expect tohave some fun doing the things it suggests. Manytimes, however, you are fooled. When you actuallytry to do the experiments you find that you donH

have or canH get the needed materials and equip-

ment. Or you find that the directions are so poorlywritten that you cannot follow them. You may evenfind the experiments won't work.

Here is a book, however, that will give you your

money's worth. If you want to do some interestingexperiments with materials you usually can find athome and with apparatus you can make easily, thisis the book for you. You will be amazed, and so willyour friends, with the magicaV tricks you can do.

Of course, science is not magic. There are certainlaws which nature follows. The experiments willhelp you understand these laws and then to explainthe magical tricks.

Mr. Wizard has done more for you than to tellyou how to do the experiments. He also has explainedwhy the experiment works. If you are interestedin science, this is the most valuable part of the book.It is easy to build a

modelairplane

orglider,

butthe most interesting thing about an airplane is, What keeps it in the air?''

You can find the answer to this and many otherquestions in this book. Mr. Wizard's explanationsare ones you really can understand. When yourfriends ask you questions about the experiments

you perform, you'll be ready with the answers.It's a ^ood book.

( i^.^>cA^^-


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Chapters

One Right in front of your nose(Air pressure)

Two Holes in the air(Vacuum)

Three What's burning?(Oxidation)

Four What makes an airplane fly?(Aerodynamics)

Five Why balance gets lost(Gravity)

Six Getting warm(Heat radiation, conduction and convection)

Seven Sound fun(Sound)

Eight The bottle, pin and soda-strawphilharmonic(Musical vibration)

Nine The case of the mysterious magnet(Magnetism)

Ten Electromagnetic magic( Electromagnetism

Eleven Charge it :(Static electricity)

Twelve The wonders of water :(Solids, liquids, gas)

Thirteen Bubbles at work :(Carbon dioxide)

Fourteen The bigest mystery of all —you :

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87

109

130

149

166

184

204

215

230

248

(The human body)Photos not otherwise creditedwere taken by Frank P. Fritzof the Popular Mechanics staff


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This is a book of science secrets. But there'smore to science than the secrets in this book. Sciencebegins with the parts of an atom, ends with the wholeuniverse and includes everything in between.

But a part of science deals with the world youcan see, hear and feel all around you. Thafs thepart of science thafs fun to investigate for yourselfright at home. Milk bottles are your flasks, glassesyour beakers and the whole house your laboratory.

Just knowing the secret isnH enough, however.You've got to understand, try and perfect an experi-ment before it will work smoothly. When it doesn'twork, figure out why it doesn't and do it again.

If you don't happen to have the exact materialsthe experiment calls for, maybe you can do it anotherway with materials you do have. No matter whatyou use to do it with, doing the experiment is thebest fun . . . and the best way to know the sciencesecret.

aO^/-m^Mr. Wizard

Dedicated to M.D.H. and H.A.R.D.and

To the scientists who showed me why . .To all the teachers who showed me how .And to all of you who want to try.


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Digitized by tine Internet Arciiive

in 2011 witii funding from

LYRASIS IVIembers and Sloan Foundation

http://www.archive.org/details/mrwizardsscienceOOinherb


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because you're used to it. You walk around in itand breathe it . . . and never think about it. Let'stake a good look at the air. I think you'll be sur-prised.

Did you know that at this very moment you'resitting at the bottom of an ocean? The air we livein is very much like an ocean. In fact, air is somuch like water you can even pour it. Here's allyou have to do:

EXPERIMENT 1

Materials: Two drinking glasses (same size)

Large basin, pail or the kitchen sink (con-tainer must be deep enough for glasses to beunder water when standing upright)

Fill the container with water and place glass Aunder water so it fills with water.

Hold glass A by the bottom and raise it out of

the water, keeping the mouth of the glass underwater. It will remain full of water. Turn glass Bupside down and put it straight down into water.Notice water does not run into glass because it'sfull of air.

Now tip the glass of air (B) under the glass ofwater (A) and see the air bubble up into the glass

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of water forcing the water out. As you pour air outof glass B, water will pour into it.

Glass A which was full of air is now full ofwater and glass B which was full of water is now

full of air. You can pour the air back and forthfrom glass to glass

You see, you pour air upside down from theway you pour water. The water makes the air vis-ible to you in the form of bubbles and makes thebubbles go up.

Did you notice that you could see the air takingup space in the glass under water? Well, the air fillsup the space around us and actually weighs some-

Glass AAir bubbli


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Glass A was full ofwater, now full of air

Glass B was full of air,

now full of water

thing, just like water does. Hold out your hand,palm up. Right on top of your hand is a tall columnof air that goes up further than you can see. Canyou feel the weight of it? Of course, you can't Yet,if the air weighs something why can't you feel it?Let's solve that mystery right now.

EXPERIMENT 2

Materials: Drinking glass

Piece of cardboard or waxed paper a littlelarger than the glass is round

Cardboard or

wax paper

^aterDrinking

glass

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Fill the glass with water to the brim and placecardboard or waxed paper on top. What's holdingthe cardboard up? The glass, of course.

Now set the glass on the palm of your righthand and place the palm of your left hand on top ofthe cardboard. Quickly turn the glass upside down,being careful to keep the cardboard in place. Nowwhat's holding the cardboard up? Your hand, ofcourse.

Cardboard or

wax paper

With your right handholding the glass firmly,

.slowly take your lefthand out from under the

cardboard. Now what'sholding the cardboardup? This is how Betsylooked when she tried itusing waxed paper.

Better try this over asink

because you're go-

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ing to make the cardboard and the water fall in aminute.

The fact that the cardboarddoesn't fall and

holds the water in the glass looks like magic, doesn't

it? Well, it isn't. It's just another example of thethings that go on all around us that look like magic.Now here's the secret of why the card doesn't fall

Remember I said that the air is like an ocean andwe're living in the bottom of it? Well, the air ispushing against the glass in all directions indicated

by the little arrows.

Notice the air pushes down on the top, in fromthe sides and from underneath up. If the glass werein an ocean, the water would push in all around thesame way. Now, while it's true that the air is push-ing in all around, the glass is rigid and keeps the air

from pushing against the water in the glass. Down

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at the bottom where the cardboard is, the air pushesup on the cardboard and it pushes up against thewater. Now you expect the water to fall becauseyou know the force of gravity is pulling it down.

But the air is pushing up harder than gravity ispulling down and, because the card is held tightagainst the glass so no air can get in and push downon top of the water, the cardboard is glued to the

glass and the water doesn't fall. What do you thinkwill happen if you let a little air in? Try it and see.Put your finger at the edge of the cardboard andpush down until a couple of bubbles of air get inand can help push down on top of the water. Thecardboard and the water in the glass will fall downjust as you expected them to.

Now do you see why you can't feel the weightof the air pushing down on your hand? You canunderstand how the air pushing down exerts pres-sure, and you just saw how the air pushes up . . .that's what held the card up to the glass. Actually,the air is pushing in from all directions . . . even fromthe inside of your hand out. Do you notice the shoesthat you're wearing? Probably not, because you'reso used to them, and that's exactly why you can't feelthe pressure of the air. You're so used to it. Youwere born and live in this atmospheric pressure.

Now see if you can solve this mystery

EXPERIMENT 3Materials: Milk bottle

Enough cheesecloth to cover the mouth of thebottle with two layers

A pitcher of water

Rubber band or string

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Pitcher

Two layers ofcheesecloth

Rubber band

Fasten a double layer of cheesecloth over the

mouth of the milk bottle with the rubber band orstring. When you fill the milk bottle with water fromthe pitcher it goes into the milk bottle very easily

because the cheesecloth is so thin.

Now set the pitcher down on the table andquickly turn the milk bottle full of water upsidedown over it. The water went through the cheese-cloth into the bottle all right. Why won't it comeout through the cheesecloth now?

It looks like the water ought to run out of the

milk bottle without any trouble because the cheese-

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cloth is so full of holes. But the cheesecloth . . . andair . . . are the keys to the solution of the mystery.

You see, the cheesecloth spreads the water over the

mouthof the

milkbottle,

preventingthe air

fromgetting in and pushing down on top of the water.But the air is still pushing up just like it did whenit held up the cardboard to the glass of water inExperiment 2. Tip the bottle a little bit and you'llsee the air flow in on the top side while the waterflows out on the bottom side of the mouth of thebottle. The gurgling sound is the result of the airand water bumping into each other as they pass.

Fran Byrne

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You probably didn't think about it but you allowfor this every time you pour anything from a bottle.You tip the bottle just enough to let the liquid runout of the bottom and the air to run in the top ofthe mouth.

Remember when you held your hand out I saidthere was a tall column of air above it going away upinto the sky but that you can't feel it because it

pushes in all directions and you're used to it? Sci-

entists have special ways of weighing the air andthey found out that it weighs quite a bit. You'veseen postage stamps that are about this big?

Well, the air on that little bit of

surface weighs 14.7 pounds. Scien-tists call it air pressure and say that

air pressure is 14.7 pounds per squareinch. To give you some idea of howmuch weight that actually is, imagineyou're carrying 15 pounds of butter.

Now the air pressure is less on the top of amountain than it is at the level of the sea becausethe column of air from the top of the mountain tothe top of the ocean of air above it is not so deep and,therefore, doesn't weigh as much. And the air pres-sure at the bottom of a mine is more than it is at thelevel of the sea because the column of air from thebottom of the mine up to the top of the ocean of airabove it is deeper. But at the level of the sea theair pressure is 14.7 pounds. Scientists call it normalatmospheric pressure. Can you imagine how itwould feel to hold out your hand and have about15 pounds of sugar on every little space the size ofa postage stamp You couldn't possibly hold yourhand up. And imagine what it would be like to try

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and stand up and walk around with all that weightpushing down on every square inch of your headand shoulders You couldn't even stand up, let alonewalk It's a good thing the air pushes in all direc-tions, including pushing out from inside of you.

When you know how to do it you can make thetremendous pressure of the air help you break astick right in two. Here's how you do it

EXPERIMENT 4Materials: Two sheets of newspaper without holes or

tears

Slats from a wooden apple or orange crate

Stout stick or baseball bat

Two sheets ofnewspaper

Hit slat

here

Wooden slat

Lay the wooden slat on a table and cover it withthe two sheets of newspaper.

Firstsmooth out

thepaper

carefully all over

the table and then with the baseball bat come down

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hard on the piece of wooden slat sticking out fromthe edge of the table. Instead of the paper and slatflying off the table as Willy expected when he triedit, he broke the slat in two right at the edge of thetable

Here's the secret of how the air pressure helpedbreak that slat in two. You know by now that theair is pushing down on top of the newspaper. Eventhough the slat is lying on the table there is still air

pushing up between it and the table. If you pushdown slowly on the slat instead of hitting it with thebat, the other end of it and the newspaper will go upbecause the air has a chance to flow in under thenewspaper and push up under the slat. But whenyou come down hard with the baseball bat, the otherend starts to go up fast That little bit of air under-

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neath expands until it's very, very thin . . . almost

nothing, in fact. It can't push very hard comparedto the air on top of the paper pushing down. Noneof the air on the outside can get in to help that thin

air push up because the newspaper prevents the airfrom getting in for a fraction of a second. So theweight of the whole column of air above the news-paper holds that end of the slat down tight withabout the same force as though there were five tonsof coal piled up there With all that pressure on oneend of the slat and you hitting the other end with abaseball bat, there's no mystery about why it breaksin two

So far we've talked about ordinary atmosphericpressure. But what happens when we somehow in-

crease the pressure of the air? All sorts of inter-esting things. For instance:

EXPERIMENT 5

Materials: A smooth tube of glass or metal about 6inches long

A wooden plunger that fits inside the tubeloosely

Slices of potato about ^4 of an inch thick

Push the tube through a potato slice and cut outa piece of potato in much the same way that you cut

out cookies with a cookie cutter. This will seal upthe end of the tube. Now do the same thing withthe other end.

Slowly push one of the potato plugs further intothe tube with the wooden plunger. Then, aimingthe other end at a suitable target, push the plungerhard and fast. There will

be aloud

pop and thepiece

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Potato ^\slice

Potato

TabU

of potato at the front end will travel like a bullet.

Simply push the remaining piece of potato tothe front end, cut a new piece of potato with the tubeand you are ready to fire again.

Notice you don't actually touch the front potatowith the plunger. The potato at each end seals theair inside the tube and when you push the plungeryou put. the air inside the tube under greater pres-sure than the atmospheric pressure around it. Asyou push the plunger the increased pressure insidethe tube builds up until it is strong enough to over-

Air under pressure

J~^_________

a=D.-)- UpV^

Plunger movesPotatobullet

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come the friction holding the front potato in the tubeand suddenly, when the pressure becomes greatenough, it pushes the potato out with considerable

force. The loud bang is caused by the sudden re-lease of the air under pressure in the tube.

When you use BB's instead of a piece of a potato,have a better compressing chamber for the air,can pump several times to build up more pressureand can release that pressure with a trigger —you'reusing an air rifle. When you put a special hammerhead on the front end and build and release strongpressure automatically, you've got an air hammer,used to drill holes, drive spikes and rivets and breakup pavements.

Using compressed air (air under compression

or pressure) you can make a water fountain.EXPERIMENT 6

Materials: Soda bottle

One-hole rubber stopper

Piece of glass tubing slightly shorter than

the length of the bottle

Short piece of glass tubing formed into anozzle

Short piece of rubber tubing to fit glass tub-

ing

Fill bottle about half full of water and place the

stopper and tubing into position.Blow hard into the nozzle. Bubbles of air will

come out of the bottom of the glass tubing becauseyou are blowing air into the tubing. When you haveblown as hard as you can, move back quickly, be-cause water will shoot out of the nozzle. How highit goes depends, on how hard you can blow.

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Soda bottle

Glass tube

You should have no trouble explaining why the

water shoots out. When you blew hard into the tubeyou forced air down through the tube and air bub-bles rose to the top of the water and were added tothe air already there. The harder you blew the moreair was forced into the bottle and the more the airwas compressed above the water. When you stoppedblowing, the pressure of the air pushed on the waterand moved it up the tube with enough force to makea fountain.

You can make a more powerful stream of watercome from a nozzle by putting more air pressure onthe water. Instead of blowing to make the pressuretry this:

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Wofer forced up

Nozzle

Compressed airforces water up

through tube

EXPERIMENT 7Materials: Soda bottle

One-hole stopper for bottle

One-hole stopper to fit water faucet

Short length of glass tubing

Short length of glass tubing fashioned into

a nozzle

Piece of rubber hose

Wire or string to make joints secure

Water in the pipe lines in the house is underpressure and you release that pressure when youopen the faucet. By holding the stopper tightly

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Compressedair

Rubbertubing

against the mouth of the faucet, the water pressurein the pipes forces water into the bottle and com-presses the air. Pinch the tube to hold the pressure

and turn off the faucet. Aim the nozzle at an ap-propriate target and let go of the tubing. The airunder pressure above the water in the bottle willpush the water out with great force.

Better try this outside because you'll need a long

range and walls and furniture aren't supposed toget wet.

EXPERIMENT 8

Materials: Soda bottle

Rubber toy balloon

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Compressed air pushesdown on water

^aier

forced out

Ever blow up a balloon inside a bottle? It's a

lot harder than you think because you'll have toblow up the bottle too

With a pencil push the balloon into the neck ofthe soda bottle, fold back the mouth of the balloonand stretch it over the mouth of the bottle.

Now blow up the balloon ... if you can. You'llfind you can't blow the balloon up very much be-cause as you begin to put air into the balloon thepressure expands it just as you'd expect. But as theballoon expands it begins to crowd the air trappedin the bottle. As you compress that air it pushesback harder and harder until it's pushing back ashard as you can blow.

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Balloon inside bottleand stretched over top

Atmosphericpressure

Sodabottle

Blow hard

Compressedair

Pressuresare equal

Compressedair

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To make the balloon bigger you'd have to blowhard enough to make the bottle bigger too. Try this

on your friends but not before you have done theexperiments in the next chapter because then you'll

be able to show them how to blow up the ballooninside the bottle without really blowing at all

While you've got the balloon handy, though, youcan ask your friends to do this

EXPERIMENT 9

Materials: A balloon

Two cups

Here's the puzzle I asked Willy: How can youpick up two cups with a balloon without using thehandles of the cups?

Arrange the cups and the balloon as I did, andblow up the balloon. As you blow, the pressure ofthe air forces the sides of the balloon into the cups.

Fran Byrne

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Fran Byrne

Still more pressure pushes the sides of the balloonagainst the inside of the cups hard enough so theywon't slip when you pick up the ballon by the neck(better use old cups as I did . . . just in case).

So whether the air is under ordinary atmos-pheric pressure or still greater pressure, it's full of

mysteries . . . until you solve them. Did you realizethat sometimes there's a sort of hole in the air?Let's investigate the amazing hole in the air scien-tists call a vacuum.

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Chapter Two

Holes in the air

Even though your friends won't be able to blowup a balloon inside of a bottle you can do it withoutblowing at all —if you make a hole in the air inthe bottle.

EXPERIMENT 10

Materials: Milk bottle

Piece of paper folded so you can slip it intothe bottle easily

Matches

Balloon

There is no need to tell you there's air around,the bottle and inside of it under normal atmosphericpressure. To make a hole in the air inside the bottleall you have to do is change some of it into somethingelse that takes up less space. That's exactly what

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Paper

Match

Milk bottle

Atmospheric

pressure

you do when you light the paper with a match andslip it inside the bottle.

As the paper burns, the heat produced expandsthe air and some of it escapes from the bottle. Whenthe air cools, it contracts; the atmospheric pressure

is greater, and the balloon is forced into the bottle.Note that some of the arrows that indicate air

pressure are missing inside the bottle because part

of the air is changed. What's left takes up less spaceand can't push as hard. We now have a hole orpartial vacuum inside the bottle. The air outside thebottle, pushing in from all directions, will try to fillup that vacuum. It's very much like when you put

your hand down into a pail full of sand and take a

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handful from the middle of it. As you pull the hand-ful of sand out the rest of the sand flows in to fill

up the hole you made. The same sort of thing hap-

pens in the air. However, the sides of the bottle arehard and hold back the air so that it can^t flow inand fill up the hole. But the balloon on top of themouth of the bottle will stretch. The atmosphericpressure pushes down and blows up the balloon in-side the bottle until the air beneath the balloon canpush back with the same force as atmospheric pres-sure.

Atmosphericpressure

Balloon

Atmosphericpressure

Atmosphericpressure

Burning paper combines with someof air creating hole or vacuum

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Atmosphericpressure

Balloon

Atmospheric

pressurepushes down

on balloon

to fill up

vacuum

Atmosphericpressure

Now youVe blown up a balloon inside a bottlewithout actually blowing at all.

When you try to get the balloon out of the bottleyou'll have to put a pencil or tube down the neckof the bottle between the balloon and the glass.

Another trick you can do with a vacuum is glue two glasses together.

EXPERIMENT 11

Materials: Two drinking glasses of the same size

Piece of paper and match

A blotter collar made to fit the rim of theglasses

Scissors

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The blotter used for the collar must be absorbenton both sides. Out of the blotter cut a circle with adiameter half an inch larger than the rim of the

drinking glasses. Then cut a large round hole inthe center of the circle to form a collar. Wet thecollar thoroughly and place it on top of one of theglasses on the table. Light the paper with a matchand hold the second glass upside down near the firstglass.

Quickly toss the burning paper in the glass onthe table and just as quickly place the second glasson the first so their rims are one above the other withthe blotter collar in between. When the burning pa-per goes out, you can raise both the glasses off thetable by picking up the top one. The wet blottercollar acts as a seal to keep out the air and the glasses

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Atmosphericpressure

Glasses gluedtogether by

atmospheric

pressure

Table

are glued together by the atmospheric pressure

trying to get in and fill up the partial vacuum inside.Before people realized that there was such a

thing as atmospheric pressure they noticed that

whenever there was a hole in the air, the vacuumseemed to suck something into it. They called it suction. And that's why you call the little rubbergadget that sticks to smooth surfaces a suctioncup. It should be called an atmospheric-pressurecup or a vacuum cup because it has no sucking powerat all. It works like this:

EXPERIMENT 12

Materials: A suction cup

Mineral oil

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Smooth surface

Atmosphericpressure

Atmosphericpressure

Hold the suction cup lightly against a smoothsurface such as a window, bathtub or tile wall.There's atmospheric pressure inside and out.

Now push it against the surface. You put pres-sure on the air inside and it escapes under the edgeof the cup.

Smooth surface

escapesAtmospheric

pressure

Atmosphericpressure

Push

Air escapes

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Smooth surface

Partial

vacuum

Atmosphericpressure

When you stop pushing, the cup springs back toits original shape because it is made of rubber. Asit does this a partial vacuum forms inside and theatmospheric pressure holds the cup to the surface.

It's a good idea to coat the bottom edge of thecup to help seal out the air. Water works, but soonevaporates. Mineral oil or petroleum jelly will do

a good job.Incidentally, every time I put up a suction cup,

I think of Otto von Guericke, who performed a veryspectacular experiment for the public back in 1650.He made two cups of metal only 22 inches in diam-eter and, in front of a great crowd of people, putthe cups together and pumped out the air from inside

them. The crowd couldn't believe its eyes when ittook eight horses hitched up to each cup and pullingfor all they were worth to finally separate them. Ofcourse, those people in those days didn't know abouta vacuum and atmospheric pressure.

Your friends won't believe their eyes either

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(an implosion is a bursting in and an explosion is abursting out).

Some of the same principles that helped youboil water with an ice cube help you make coffee.

*

EXPERIMENT 14

Materials: Vacuum coffee maker

Coifee

Water

Source of heat

(Cups, if desired, for drinking coffee whenexperiment is over)

Instead of waiting for the coffee to be made,let's watch it while it's being made.

Air pressure

Glassstrainer

Boiling

water

^VWWWiAAA^Heat

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Air pressure

Coffee

Steampressure

/WWWVVWW^̂— Heat

Atmospheric pressure is all around, of course.But we're especially interested in the downwardpush through the coffee and onto the top of the waterin the bottom pot. As the water boils, it changes tosteam which takes up more room. Pressure developsand the water is forced up the tube past the strainerto mix with the coffee.

When you turn off the heat, the steam cools off,changes back to water and a partial vacuum formsin the lower section. The atmospheric pressurepushes the water down, the strainer holds back the

coffee grounds as the water (now coffee) starts downthe tube.

When all the coffee has been pushed back intothe lower section, there is a sucking noise and bub-

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Atmosphericpressure

Coffee

bles come out of the tube. But atmospheric pressureis an old friend by now and you know the bubblingsound is that old friend filling up what's left of thepartial vacuum above the coffee.

And if you drink coffee, and got the cups outbefore, thank that old friend, atmospheric pressure,for helping you make it.

A vacuum helps you in lots of other ways besidesmaking coffee. You should be able to glance aroundthe room and find lots of vacuums (vacua, to be cor-rect) at work.

Can you see a thermos bottle or a vacuumcleaner? How about concentrated fruit juice? The

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Atmosphericpressure

Coffee

grounds

Coffee

Air pushes in at end of coffee maker,causing bubbles and gurgling

water in the fresh juice is boiled away in a vacuumto keep the temperature low enough to preserve theflavor and vitamins in the juice. You did the samething when you boiled water with an ice cube

The implosion I cautioned you about at the timeis harmless but dramatic if done with a gallon tincan

EXPERIMENT 15

Materials: Gallon tin can with screw top

Pitcher of water

Source of heat

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Atmospheric

pressure

:jri

y/^ Visible cloudsjj of water vapor

Steam

pressure

^Z2ZZ2ZZZZ222Z^

>VVVVV\

Cover off

Hater

Heat

Atmosphericpressure

Ln. ^3Screw top

on tight

Partial

vacuum

'rrrrrrryr^r^r,

Atmosphericpressure

Water

Pressures

nearly

equalized

Atmosphericpressure


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The can that works best is the rectangular kindthat varnish comes in. Remove the screw top, pourin about a half a cup of water and place it on thestove. When you can see wispy clouds of watervapor coming from the top you know this is the sit-uation inside:

All the air has been forced out of the can and thepressure of the steam on the inside balances the pres-sure of the atmosphere on the outside. When youremove the can from the stove and screw the top ontight this happens:

The steam cools, changes to water, a partialvacuum forms inside and the atmospheric pressurestarts to squeeze. You can help the squeezing bypouring cold water over the can to make it cool offfaster. With a twisting and groaning the can iscrushed by the air until the pressure is nearly equalagain.

A hole in the air can be a very useful or damag-ing thing with atmospheric pressure all around usthe way it is. If you don't believe it, look:

Fran Byrne

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Chapter Three

What's burning

We haven't investigated air's most importantsecret. In fact, without this secret ingredient you

wouldn't be able to live at all. Let's find out some-

thing about it.

EXPERIMENT 16Materials: Dish of water

Candle in holder

Milk bottle

Matches

Set the candle and holder in the water so thatfive or six inches of it is above the surface of the

water. Now light the candle and hold the milk bottleready to put over the candle.

When you put the milk bottle over the candle,the candle continues to burn for a short while. How-ever, the flame gets lower and lower and finally goes

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Milk bottlefull of air

Water

out and the water in the dish rises into the neck ofthe milk bottle.

As the candle burned, it united with the secretingredient of the air: oxygen. When the supply ofoxygen in the air in the bottle ran low, the candlewent out.

Light the candle and place the funnel over it as

Atmosphericpressure

Partial vacuum

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you did the milk bottle. Because the funnel has a

hole in the top you might expect the candle to burn.

However, it goes out just as it did when you put themilk bottle over it

EXPERIMENT 17

Materials: Dish of water

Candle and matches

A large funnelPiece of tubing

Candle goes out

Candle in holder

Here's why the candle goes out even thoughthere's a hole in the funnel. When the oxygen in theair inside the funnel combines with the materials inthe candle to form a flame, hot gases result which goout the chimney of the funnel. While the gasesare going up, very little new air can come downthe chimney. Unfortunately, by the time the aircan get down into the chimney, the candle is out.We've got to bring the air in another hole near thebottom of the candle in order for it to burn. Here's

how to do it without punching a hole in the funnel

:

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Gases out

Air in

To the inside of the funnel, attach a rubber tube

with tape. Make sure that the mouth of the tubeis above the level to which the water will come whenyou put the funnel into the water. Now light thecandle and place the funnel over it as before. Thistime air will be able to go up in the tube around thecandle flame, supplying it with the necessary oxy-

gen. The gases go out the chimney at the top asthey did before. Incidentally, be sure when you putthe funnel and tube into the water that you allowno water to get into the tube because it will blockoff the passage of air and the candle will go out.Notice that with or without the tube, water does notrise in the funnel as it did in the milk bottle. Thereason it doesn't, of course, is because there was nopartial vacuum formed by the burning.

What you've actually done with the funnel andthe tube is to create a draft very much like thatin a furnace. There's an opening for new air toget to the fire and an opening for the gases to escape.

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This happens every time a candle burns —the heatin the flame of the candle sets up currents whichsupply it continually with oxygen from the air.

That's what all burning is —a chemical processof combining something with oxygen accompaniedby heat and light, like this

Fran Byrne

What I use to make a large flash like that is aspecial kind of paper treated so that it will burn up

completely in a flash. In other words, it com-

bines with the oxygen in the air to form nothing but

gases and no ashes at all. It's called flash paper andcan be purchased from a magic store. Other mate-

rials combine with the oxygen in the air too but notquite so easily as flash paper. Ordinary paper, forinstance, burns fairly readily as do some kinds ofwood. Coal, on the other hand, is a little harderto get started and steal is harder yet . . . unless youknow how to do it. To make steel burn, let's look

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at paper first. Have you ever put a whole dailynewspaper all folded up into a fire? The top fewsheets burn quickly but some of the inside sheets

may not burn at all because they're not gettingenough oxygen. When you crumple paper into aball all parts of it get more oxygen and it burnseasily. You do the same thing with wood but, ofcourse, you can't crumple it so you split it up intokindling. Coal is pretty hard to start, but when

you grind it into a powder it burns without anytrouble at all. In fact, coal dust in mines can bevery dangerous because sometimes explosions re-sult. The same thing is true with steel. If you heatit up enough and give it plenty of oxygen it willburn. Here's how you can burn steel at home.

EXPERIMENT 18Materials: Candle in holder

Matches

Toothpick

Steel wool

Toothpick

Candle

Steel

Iron oxide

sparkles

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Simply roll up a small quantity of steel woolinto a loose bundle on the end of the toothpick. Then

hold the steel wool in the candle flame and you'll seetiny sparklers of burning steel fall to the table.

The small sparklers are pieces of steel combin-ing with the oxygen in the air to form a new com-pound called iron oxide. You have actually burnedsteel.

Steel and iron and lots of other things too areoften doing a slow burn around your house allthe time. There's not much heat given off nor anylight at all so you don't call it burning. Insteadyou call it rusting. Oxidizing is a more scien-tific way of saying the same thing. When iron orsteel rusts it combines with the oxygen in the airlike the candle did in the milk bottle. Let's do some-

thing like we did then and see how much oxygen ittakes to rust —or oxidize —steel.

Moistened

steel wool

Atmosphericpressure

Drinking glass

\Nater

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EXPERIMENT 19

Materials: Steel wool

Medicine bottle

One-hole rubber stopper to fit bottle

Glass tubing to fit rubber stopper

Drinking glass with water in it

Moisten the steel wool with water and place itin the bottom of the medicine bottle. Then put thestopper and tubing into it and set it in the wateras shown in the drawing on the opposite page.

Wofer has risen

in tube as steel

woo/ combineswith oxygen

in air

The oxygen in the air inside the bottle will slow-ly combine with the steel wool to form iron oxide inmuch the same way as when you burned the steelwool in the candle flame. However, the process willgo on much more slowly and you won't be able tosee it. But watch the column of water inside the

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glass tube. As the oxygen in the bottle combineswith the steel wool, it no longer takes up as muchroom as it did before and a partial vacuum will beformed. Atmospheric pressure will push the waterinto the tube to fill up that partial vacuum and ina day or two your apparatus will look like the draw-ing on the previous page.

So you see steel will combine with the oxygenin the air if water is present and you give the reac-

tion enough time.When you want to get rid of a basket full of

waste paper you can take it out in the back yardand burn it. Part of the paper changes to a gasthat you can't see when it combines with oxygen inthe burning process. Wouldn't it be real handy

to be able to get rid of an ink spot on a piece of clothby combining it with oxygen and changing it into amaterial you can't see? You can't burn it up be-cause you'd burn up the cloth too. Let's do it byusing oxygen, not from the air, but from waterYou see, water is made up of hydrogen and oxygenso we have a supply of oxygen available in water.Instead of using a cloth to put an ink spot on, let'sset up the materials so we can do a magic trick.

EXPERIMENT 20

Materials : Two drinking glasses

Water

Ink

Bleach (like Chlorox)

Fill one glass half full of water and add enough

ink to color it. Put a few drops of bleach (like

Chlorox) in the bottom of the other glass. To yourfriends the second glass will look empty. Call atten-

tion to the fact that the first glass has wine in it.

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Just enough ink

in V2 glass of

water to color

itFew drops of

bleach(likeChlorox) in

bottom of

glass

Then, with the appropriate magic word,''Oxidation, pour the ink water into the other glass.The color will disappear . . . and you've changed''wine to water

Pour ink water intoother glass and color

disappears

The trick of changing wine to water is asold as magic itself

—but it's not magic at all. You

know oxygen is what does it. How the oxygen getsout of the water is a lot more interesting than thetrick. Here's how it happens: the bleach containsthe element chlorine which, when added to water,combines with the hydrogen in the water, freeing

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Cut the lemon in half and you've got your secretink well. Jab the clean pen into it until you haveplenty of lemon-juice ink on the pen. Now, writ-

ing with fairly bold strokes, print whatever messageyou want on the paper. When the lemon juice driesit will be invisible. You can use vinegar, too, butit doesn't work as well as the lemon juice. I showedWilly a blank sheet of paper on which I had writtena secret message. When he found out what he hadto do to make the writing appear —and did ithere's what he saw:

Ben and Sid Ross


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don't think it's spectacular, look at Betsy when shetried it.

You can hold a large piece of the same resinin the candle flame and nothing much happens. It'llget warm and melt but won't catch on fire easily.Yet the same resin when powdered gets plenty ofoxygen from the air around it and burns with a

flash.The same thing will happen to flour when the

conditions are right. Now, don't worry, the floursitting in the can on the shelf in the kitchen won't

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blow up because the conditions aren't right. Here

are the right conditions:

EXPERIMENT 23Materials : Canister or paint can

Candle in holder

Matches

Dry flour

Small funnel

Piece of rubber tubing

Tablespoon

Arrange the equipment like this:

Canister orpaint can

Blo\

Rubbertubing

Holding a tablespoon of flour in one hand, lighta match with the other and slowly put the burning

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match right into the flour in the tablespoon. If youexpected the flour to burn, it won't. It puts the

match out instead, because it shuts off the supply

of oxygen to the match. Put the same tablespoonof flour in the funnel in the bottom of the can. Lightthe candle and place it on the bottom and put thecover on tight. Blow hard into the tube and you'vegot a spectacular explosion


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Don't worry too much about it though. Theexplosion isn't very dangerous if you keep your face

away from the flame that comes out of the top ofthe can. Keep an eye on the can cover too. Youdon't want it to fall on you. Even if it does it can'thurt very much.

Can you understand from your experiment withthe resin why you have an explosion when you blowinto the tube? The tablespoon of flour didn't burn

when you put the match into it because it couldn'tget enough air, but when you blew hard into thetube you spread the flour throughout the air insidethe can. Each tiny particle has a lot more air (andthe oxygen in the air) around it. The flour nearthe candle flame was heated up enough to burn. This

burning heated up more flour, more burned, andso on. All this happened very quickly, of course.The gases formed when the flour burned all at onceand blew the cover right off the top of the can.

Burning or combining things with oxygen withheat and light being given off can be helpful orharmful. When the fire is in the furnace, that'sgood, but when the fire is burning up the house,that's not so good.

How can you control burning? Let's find outwhat it's all about so you'll be able to prevent harm-ful fires before they start or help put them out quick-ly while they're still small.

One way you can put out a fire is to shut offits supply of oxygen. Remember what happenedwhen we put the milk bottle over the candle? Youcan put out a fire in the same way. Smother it witha rug or a damp cloth or anything that's handy aslong as it will shut off the supply of oxygen.

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Now if we could shut off a fire's supply of oxy-gen with something that's invisible, it would lookrather strange to see fire go out all of a sudden,

wouldn't it? You can do it with no trouble at all.

EXPERIMENT 24

Materials: A sheet of paper

Candle in holder

Matches

Baking soda

Vinegar

Drinking glass

Small piece of cardboard

Make the paper into a trough that will rundown to the candle in this way:

Troughof paper Burning

candle

Now pour half a cup of vinegar into the glassand add a heaping teaspoon of baking soda.

There'll be a chemical reaction in the glass. Wait

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Heaping teaspoonof baking soda

Drinking

glass

Half cupof vinegar

a few seconds and then cover the glass with the piece

of cardboard. The chemical reaction will fill up theglass with carbon-dioxide gas. It's invisible so don't

Cardboard

Invisible

carbon-dioxide

gas

bother looking for it. You can put out the candle bysimply pouring the invisible gas (not the liquid)

down the paper trough.You've shut off the supply of oxygen from

around the candle flame by pouring carbon dioxideon it. That's why the candle goes out. By the way,we'll do a lot of other interesting experiments with

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Pour carbon-dioxidegas down trough

carbon dioxide in Chapter 14. Firemen make car-bon dioxide with special equipment which you'll findout about later.

Now making carbon-dioxide gas and with itputting out fire is fine as long as the fire is on the

floor. The gas is heavier than air and sinks to thefloor. But what about when the wall's on fire? Let'smake bubbles of carbon-dioxide gas in a sticky-liquid that firemen can shoot at the wall. It sticks

to the wall and smothers the fire. It's called firefoam.

EXPERIMENT 25

Materials: Licorice extract

Aluminum sulphate

Baking soda

Drinking glasses

Water

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Two teaspoonsaluminum

sulphate in

one cup water

L icoriceextract

solution

Make two solutions in the following way: First

solution: two tablespoons of aluminum sulphate toone cup of water. Second solution : add licoriceextract to about a half cup of baking soda until youget a thick paste. Then to this add an equal amountof water and stir until it's dissolved. When youhave the two solutions prepared, pour a little of eachat the same time into another glass. Here's whathappened when Willy and I did it:

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United Press

The fire foam you see is filled with little bubblesof carbon dioxide. The tough film around eachbubble and the carbon dioxide inside smother thefire.

Of course, the best general fire fighter is water,and you should be able to explain why by now. It

doesn't smother the fire very much but you knowthat things burn only when they get hot enough.Remember the paper, wood and coal all have to beheated up to high enough temperatures before theywill combine with oxygen or burn. Water cools offthe burning building and lowers the temperatureto the point where the wood will no longer burn andso the fire goes out. Another reason is that waterpoured on a fire creates steam, which shuts off oxy-gen around the flames. It's very important, too,that a good supply of water be available in hydrantsready to be used whenever the firemen need it.

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Chapter Four

What makes an airplane fly?

You've seen lots of airplanes up in the sky.Maybe you have even been inside of one as it tookoff from the ground and climbed high up among theclouds. What makes that airplane fly? You cansolve that mystery for yourself with the help of a

wood screw and an atomizerFirst, an airplane has to move and that's what

the propeller is for. Let's make a propeller thatmoves.

EXPERIMENT 26

Materials: Tin from a tin can

Small tack

Light-weight stick or dowel

Light string or thread

Tin snips or old pair of large scissors

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Cut a piece of tin from a tin can, pound it flatand, with a pencil, draw a propeller like this on it

Punch hole

Cut out of tin can

Cut the propeller out and punch a small hole inthe center. Then wind the string or thread tightlyaround one end of a light-weight dowel about 6inches long. This is to prevent it from splitting when

Small tack

L ight string

L ight-weightstick

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you place the propeller on the end of the dowel andfasten it securely with a tack. Twist the blade ofthe propeller in opposite directions and you're ready

to go. Hold the dowel between the palms of yourhands. Move one palm forward and the other palmback, twirling the stick and quickly take your handsaway.

The propeller will pull itself right over yourhead. By bending the blades of the propeller to theright angle you can get the propeller to go quite high.

With the help of an ordinary spool you can makea propeller that will go higher yet.

EXPERIMENT 27

Materials: Spool

Tin propeller similar to the one in the last

experiment

Small brads or finishing nails

Piece of wood for a handle

Knife

Piece of stout string

At one end of the piece of wood carve out around peg slightly smaller than the hole in the spooland slightly shorter than the length of the spool.Space the two brads evenly between the hole and theoutside edge of one end of the spool and pound themdown part way. Cut a propeller out of tin as in the

previous experiment, but this time punch two holesin it to match the brads in the spool. The holes mustbe big enough to allow the propeller to slip off thebrads easily.

Wind just enough string on the spool so youcan pull it all off easily when you hold the flying ma-

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What about a jet plane? It has no propeller.What pulls or pushes it through the air? You'll findyour answer in a toy balloon.

EXPERIMENT 28

Materials: Toy balloon

Blow up the balloon and pinch the mouth shutwith your fingers. As you blew, you forced air insidethe balloon and it pushed against the sides of theballoon making it bigger. The pressure of the airinside the balloon is equal in all directions.

What will happen when you suddenly let go of

the neck of the balloon? Let's see why it happens

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Balloon

Air pushing

equally inall directions

Balloon moves

this way

Balloon

Air escapes

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before you try it. When you let go, the air inside theballoon is released at the mouth and suddenly thepressures inside the balloon aren't equal in all direc-

tions any more. There's a hole where the air insidethe balloon can escape instead of pushing. The airpushing against the front of the balloon isn't bal-

anced by the air pushing against the back, so the airin front pushes the balloon forward.

Of course, a jet plane doesn't have a balloon in-

side of it. It burns special fuel in a special enginethat sets up pressures like those inside the balloon.The unbalanced pressure at the front of the jet en-gine is what drives a jet plane forward.

Why should an airplane move anyway? Seemslike a silly question. To go some place, of course.But the fact that a plane moves through the air iswhat keeps it up. You will understand all about thatwhen you have done five little mysteries, all basedon the same principle.

Do each one of them and then we'll solve themall at once.

EXPERIMENT 29

Materials: Strip of thin paper about 12 inches long and2 inches wide

Hold the end of the paper with one finger underyour nose and blow through your mouth. You expectthe paper to rise. The air you blow hits the paper

and forces it up as shown in drawing on oppositepage.

EXPERIMENT 30Materials: Same as preceding experiment

Now hold the paper against your chin and blowhard. Betsy was surprised when the paper went up.

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You expected the paper to go up when you blewunder it. Why does it go up when you blow over ittoo? That's one of the little mysteries. Here's an-other:

EXPERIMENT 31

Materials: Sheet of stiff paper or thin cardboard about

4 inches by 8 inches(A filing card works fine)

Fold the ends of the cardboard over to right

angles one inch from each end.

Place the cardboard arch on the table and

blow hard under the arch trying to blow it over.

Blow under cardand flip it over

TYou'll find that the harder you blow, the harderthe cardboard sticks to the table. Why can't youblow the cardboard over? When we've solved that

mystery we'll know why an airplane flies.

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pin keeps the cardboard from moving sideways.Holding the spool with the cardboard aimed at theceiling, blow through the other end of the spool. Seeif you can make the cardboard square hit the ceiling.

You'll find you can't blow the cardboard squareoff the spool no matter how hard you try. Why?

EXPERIMENT 33

Materials: Two sheets of writing paper

When you blow down between the sheets of paper,a surprising thing happens. Instead of being blownapart, as you would expect, the sheets come together.

Blow

Sheets

of paper

movetoward

each other

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EXPERIMENT 34

Materials: Vacuum cleaner with hose for attachments

Balloon with wire weight

Table-tennis ball

Blow up the balloon, tie it off and add enoughwire to weight it. With the hose attached to theblower end, turn on the vacuum cleaner and hold thehose straight up. Carefully place the table-tennis

ball in the middle of the stream of air. The air com-ing out of the hose pushes up on the table-tennis ballhard enough to hold it suspended in mid air. Placethe balloon above the ball in the air stream. It will

be suspended in mid-air too.

Toivo Kaitila

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Balloon Wire forweight

Direction

of air flow

Table-tennisball

Blower end ofvacuum cleaner

Now, why don't the table-tennis ball and theballoon roll off to the side of the column of air andthen fall down? You can even move the mouth ofthe hose slowly from side to side and the table-tennisball and the balloon will move with it. What holds

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them in the middle of the stream of air? If you arepuzzled, don't worry. Willy was too when he tried it.

Now, let's solve all these mysteries at once . . .with an atomizer

EXPERIMENT 35

Materials: Two glass tubes

Drinking glass half full of water

Low pressure

Water

Before blowing,

water in tube

was at thislevel

Place one glass tube into the water in the glassand the other at right angles so the ends of the tubesare close together. Now blow into the horizontaltube.

Before you started blowing, the level of the

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water in the vertical glass tube was the same as thewater in the glass because atmospheric pressure

pushed down on the water in the tube as well as onthe water in the glass. When you blow through thehorizontal tube the air moving across the top of thevertical tube can't push down as hard. An area oflow pressure or partial vacuum forms at the top ofthe vertical tube. Atmospheric pressure on thewater in the glass pushes down and forces the waterup the vertical tube to fill up the low-pressure area.When the air is moved by squeezing a rubber ballinstead of blowing, perfume is used instead of water,and the length of the vertical tube is adjusted so theperfume is pushed all the way up to meet and bescattered by the moving air . . . then you have a

perfume atomizer. What's a perfume atomizer gotto do with why an airplane flies?

First, let's see how an area of low pressuresolves the five little mysteries and then the big mys-tery of what makes an airplane fly. In each of thefive little mysteries you speeded the air up by blow-

ing or by using the blower end of a vacuum cleaner.The pressure of the air (atmospheric pressure) try-ing to fill up the area of lowered pressure is whatmade the paper rise, the card stick to the table, thecardboard stay on the end of the spool, the papers gotogether, and the table-tennis ball and the balloonto

stayin

the air stream.

Air pressure

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Air pressure

BU

Lov/'Pressure areaAir pressure

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Now we're ready to solve the big mystery ofwhat makes an airplane fly.

You found out how a propeller or a jet enginemoves an airplane through the air. The air flowspast all the parts of the airplane just as though theplane were standing still and a giant were blowingin front of it. Let's pretend to cut a wing in half asthe plane is flying and see what's going on around it.We are going to investigate this part of the airplaneright here.

II

II

I

Let's get closer to the cross section of the wingand imagine you can see how the air flows around it.(Remember the airplane is pnlled through the airby the propeller; the propeller doesn't blow the air

over the wing.)When you held the strip of paper under your

nose and blew through your mouth, the paper wentup as the air hit it. The same thing happens to thebottom side of the wing as it moves through the air.The air hits it and forces it up. You feel the sameforce when you are riding in a car and put your handout of the window. When you hold your hand atabout the same angle as the wing is attached to theairplane, your hand is forced up by the air. Aboutone-third of the force necessary to hold the plane inthe air comes from the moving air hitting the bot-tom of the wing.

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Direction of

air flow

L owpressurearea

Now let's look at what's happening along thetop of the wing. The wing is shaped in such a waythat the air blowing over the top has further to go

and so is speeded up. By now you know what hap-

pens when air is speeded up. An area of low pressureforms. The atmospheric pressure pushes up underthe wing trying to fill up that lowered-pressure areaand, in so doing keeps the airplane up. About two-thirds of the force necessary to hold the plane in the

air comes from the air pressure trying to flow to the

areaof

lowered pressure.Why not see for yourself how it works by mak-ing a wing section out of paper?

Paste the ends of the strip of paper togetherlike this

Strip of paper2 wide X 8 long Paste here

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EXPERIMENT 36

Materials: Strip of writing paper about 2 inches wide

and 8 inches long

A dab of paste or glue

Pencil

Place your paper wing on the pencil and blowacross the top. The same thing will happen to your

wing as happens to a real one; it will fly. Don'tforget, you're making the air flow over the wingby blowing. The air really flows over the airplanewing because the plane is moving through the air,pulled by the propeller or pushed by a jet engine.

Blow L ow-pressurearea

Paper wingrises

So you see, we solved, with a wood screw andan atomizer, all the five little mysteries and the bigmystery of what makes an airplane fly.

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Chapter Five

Why balance gets lost

What is up, anyway? The easiest answer foryou, probably, is to point your finger to the sky andsay, That's up. But if you continued that samedirection down through the earth until you cameout on the other side, you'd be pointing down So up is a direction, all right, but with some qualifica-tions. Let's look at what some of those qualificationsare.

Up is the opposite of down. Nobody willargue about that. Down is the direction thingsmove when they fall. In other words, things arepulled toward the earth by the force of gravity and

the direction in which they move is down. Upbeing the opposite of down means up is awayfrom the earth. That's why you point your fingerat the sky and say, That's up. Just so it will beclear in your mind you can do a very simple experi-ment.

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EXPERIMENT 37

Materials: Grapefruit

Toothpicks

Plunge the toothpicks into the grapefruit at

different points. Where you put them really doesn'tmatter as long as they stick out straight. The otherend of each toothpick will be pointing up. So the

answer to the question of What is up? is, Up isaway from the earth; down is toward the earth.The reason for the difference between up and downis the force of gravity. Let's look at it.

But you can't see the force of gravity. How-ever, you can see what the force of gravity does, soyou'll have to investigate that.

You know the force of gravity pulls you toward

the earth. Doesn't it sound logical to assume thatthe heavier an object is, the faster it will be pulledtoward the earth? A long time ago many peoplethought so. Then a man by the name of GalileiGalileo, who did many experiments in many fieldsof science, did an amazing thing. He proved it wasn'tso. This is the way he did it:

EXPERIMENT 38

Materials: Grapefruit

Orange

Hold the grapefruit and the orange in front ofyou at about eye level so that they are at the sameheight. Then let go of them both at the same time.Which will hit the floor first, the grapefruit or theorange? Here's what happened when Betsy tried it.

Which hit first, the grapefruit or the orange?If both started falling at the same time, they both

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hit the floor at the same time That's why you prob-ably had trouble telling which one hit first.

This simple experiment is important for sev-

eral reasons. When Galileo first did it, it showedthat the people who believed that the heavier anobject was the faster it would fall, were wrong. Andsecondly, it pointed out the importance of proving

by trying —by experiment —the ideas people hadabout the world around them. Previous to that time

many philosophers only thought and talked aboutthe things around them without actually lookingand trying experiments. Galileo, however, did manyexperiments and proved with them that the conclu-sions he came to actually fit the facts. He didn't usea grapefruit and an orange when he did the experi-ment you and Betsy did. He used metal balls ofdifferent weights and is supposed to have droppedthem from a leaning tower in the town of Pisa, Italy.Here's a picture of it.

The leaning tower of Pisa, like Galileo's experi-ment, is interesting for two reasons too. First, youcan imagine Galileo standing on the balcony drop-ping the light ball and the heavy ball and the amaze-ment of the people when they saw them both hit theground at the same time. Secondly, as you look atthe tower you will notice that it is leaning over quitefar Why doesn't it fall over? Before we're throughinvestigating the force of gravity, you'll understandwhy the leaning tower of Pisa continues to lean and

not to fall.

Before we do that, however, let's do anotherexperiment like dropping the grapefruit and theorange but this time get different results.

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EXPERIMENT 39

Materials: Small balls of cotton

Thread

Small sheets of tin or aluminum foil

Make little balls of cotton as nearly the samesize as you can. Cut out from a sheet of tin or alu-minum foil, two identical squares. With the thread

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tie the cotton balls to the sheets of tin foil, like this:

Ball of cotton T hread

Sheet of tin foil

Drop Drop

Hold the two sheets of tin foil with the cottonon top of them about eye level and drop them at thesame time as you did the grapefruit and the orange.Which hits the ground first?

Both will probably hit at pretty close to the same

time as you would expect from your previous ex-periment. Now do this, however. Leave one of thecotton balls and tin foil just as it is. Take the otherone and roll the tin foil around the piece of cottonso that you have a little ball with cotton inside andtin foil around the outside.

Now hold them both at eye level and drop them,as you did before. Which one hits first? This time

T infoilpressed

around

cotton

Cotton

Drop

Drops faster

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you will find that the little ball of cotton and tin foilwill hit the floor first. You have added no weight.Are you defying the laws of gravity? Not at all,

because you have to take something else into con-sideration this time.

Remember in Chapter 1 we found that the airwas like an ocean and you're living at the bottom ofit? Well, if you drop an object in the ocean you canunderstand how the water has to flow around it as itfalls to the bottom. The air, too, has to flow aroundan object that moves through it. The moving objecthas to push the air out of the way. Because bothpieces of foil and cotton weigh the same, gravity ispulling them down with the same force. The flatpiece has a lot of air to push out of the way whilethe rolled-up piece has little air to push out of the

way because it's rolled up. That's why the rolled-uppiece hits the floor first. It's sort of streamlined to

reduce air resistance.

You could prove it's the resistance of the airthat makes the difference by dropping both piecesin a vacuum. If you did, you'd find that they'd both

fall at exactly the same rate. However, a vacuumgood enough to do that sort of experiment is prettyhard to make at home, so here's another way ofdoing it.

EXPERIMENT 40Materials: A book

A sheet of paper a little smaller than thecover of the book

Place the paper on top of the book so that noneof the edges of the paper stick out over the edge of the

book. Then hold the book up about eye level and

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drop both the paper and the book at the same time.You will notice that they stay together all the waydown which means that they must drop at the samerate. You see, here's what happens

Book

Air flows

As the book falls through the air, the air ispushed aside as indicated by the arrows. That meansthat the light-weight paper that would ordinarilyflutter to the ground has the air pushed out of theway in front of it by the book. The paper can nowdrop as fast as the book does. That's why both thebook and the paper hit the floor at the same time.

While the book's there on the floor, step back

one full step. Pick up the book. Here's Willy try-ing it:

Willy couldn't pick up the book without fallingover and you won't be able to either. Why?

Here's another puzzle: how could you balancea cork and two forks on the point of a needle?

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Ben and Sid

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The solution of the puzzle of how to balancetwo forks and a cork on the point of a needle is reallyanother puzzle. Why do the cork and the two forksstay balanced on the point of the needle? To under-stand why, you have to play with blocks. Here'swhat Willy and I used to solve the puzzle of whyhe couldn't pick up the book and why the cork and

*two forks balanced on the point of a needle. You canmake your own equipment out of anything around

the house.EXPERIMENT 41

Materials: A block of wood

Some tacks

A hammer

Some string

Into at least three of the sides of the block of

wood pound a tack part of the way into the wood.Next tie the string to the head of the tack and hold

the block of wood up so it can hang freely.

String

Center ofgravity

Line throughcenter of

gravity

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Notice that the block of wood comes to rest in aposition that depends on where you put the tack.

If you pretend to draw a line straight down from thestring it would look like the dotted one in thedrawing. Now put the string on one of the othertacks and hang the block up again. If you pretendto draw a line straight down from the string, thissecond imaginary line will cross the first one some-place inside of the block of wood.

Wooc/en block

Center ofgravity

I

- L ine through' center of

I gravity

The place where the two imaginary lines crossis called the center of gravity of the block because

that is where the force of gravity seems to be pull-ing on the block.

Now hang the block up by a third tack. Pre-tend to draw a line straight down from the stringand you'll find the third imaginary line goes rightthrough the other two at the center of gravity

What are we trying to prove with the hanging

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MR WT7APn'S

Center Tack Str ng

/ N >1 -/ /̂-</ /' / Tack

Center ofgravity ^ 1 .Line throughcenter ofgravity

block and all these imaginary lines? Simply this:that when an object is held up at only one point theforce of gravity will automatically line up the center

of gravity of the object directly under the point ofsupport. No matter where you put the tack andstring, when you hold the block up by the string thecenter of gravity is directly under the string. Whydo we want to know about the center of gravity?Because it's important to understanding why you

can't pick up the book without falling over and whythe cork and two forks balance on the point of aneedle. But we've got to do one other experimentbefore we can understand those two puzzles.

EXPERIMENT 42

Materials: Block used in the above experiment

Same string

A small weight

A table

A piece of wood four or five times as long asthe block

Put a tack on one of the large surfaces of the

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block directly above the center of gravity. To thistack, tie the string, and at the other end of the stringtie a weight. Then put the piece of wood on the edgeof the table and place the block near the center ofthe wood so that the weight hanging from the stringcan hang over the edge of the table. Now pick upthe piece of wood and slowly raise one end of it.

How high will you have to raise the piece ofwood before the block will fall? Notice that as long

as the vertical line through the center of gravity(represented by the string with the weight on it)falls within the base of the block, the block does not

fall.

But as you gradually raise the piece of wood,note what happens when the string moves outsidethe base of the block. As soon as the vertical line

Center ofgravity

Table

We/g/jf

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Block topples

through the center of gravity falls outside the base

of the block, the block topples over.

The two experiments you have just done canbe summed up like this: any object will be at restor balanced when it is suspended from a point di-rectly above or below its center of gravity, and anobject will remain at rest or balanced as long as thevertical line through its center of gravity remainswithin the area supporting it.

Now look at the leaning tower of Pisa again.A vertical line through its center of gravity evi-dently lies within the base of the tower. That's whythe leaning tower of Pisa continues to lean and notto fall.

Now can you understand why you can't pick up

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the book when you toss it on the floor and take onestep back from it? Your center of gravity is some-where in your midsection, probably somewhere be-tween your hips or a little higher. You have notrouble balancing yourself as long as the vertical

line through your center of gravity remains overyour base —your feet. But the minute you try tolean forward your center of gravity is going to startmoving because you are bending. You automaticallytake care of this shifting of your center of gravityby moving your hips back so that your center ofgravity still remains over your feet.

^hen you try to lean over further yet, however,the vertical line through your center of gravity grad-ually moves forward more and more until it is no

longer within the area of your feet. At that pointLine through

center of

gravity

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you lose your balance and fall forward. So when youlose your balance, you '^lose the vertical line

through your center of gravityThe clowns with the big feet at the circus can

lean very far because they wear enormously longshoes. They can lean over further than you can be-cause the vertical line through their center of grav-ity remains within their long base.

The center of gravity of the block was an imag-inary point inside the block and most of the timeyour center of gravity is inside you. But sometimesit can be outside of the thing that's balanced. Whenyou balanced the cork and the two forks on theneedle, the center of gravity actually was not in thecork or the forks As soon as you balance them onthe pencil, you know the vertical line through the

Cork

Fork

Fork

is point of support

I

Line through\ir center of

gravity

Pencil

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center of gravity must go through the point of sup-port. The center of gravity of the forks, cork andneedle must be below the point of support . . . insidethe pencil If you think the center of gravity isabove the point of support, try putting the needle

in the other end of the cork and balancing them.You'll find it very difficult to keep the vertical line

through the center of gravity going through such asmall point of support. The whole thing will fall,so get your hands out of the way. You don't wantto be jabbed by the needle

With the center of gravity below the point ofsupport, the cork and forks are so well balanced youcan gently push one of the forks and the whole thingwill spin —on the point of the needle

Here's a rocking pencil and knife based on thesame idea.

EXPERIMENT 43

Materials: A wooden pencil

A pocket knife

Open the large blade of the pocket knife so thatit forms a right angle to the handle. (Careful, don't

cut yourself.) Push the point of the blade into thepencil near the sharpened end. Balance the pencil

and the knife near the edge of the table so the handleof the knife can go under the edge of the table.

Can you find the point of support? That shouldbe easy: the point of the pencil. Can you find thecenter of gravity? That shouldn't be too hard eitherbecause you know that it must lie above or belowthe point of support because the knife and the pen-cil are balanced. In this case, because of the weight

of the knife, you can assume that the center of grav-

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Pencil

TablePocket knife

Line throughcenter of

gravity

ity is probably someplace in the handle of the knife.

When you have the pencil balanced you can givethe knife a gentle shove and both the pencil and theknife will rock back and forth with ease.

Remember Humpty Dumpty who fell off thewall and couldn't be put together again by all theking's horses and all the king's men? That's whatBetsy thought of when she saw an egg peering overthe edge of the table.

When Betsy wanted to know why HumptyDumpty didn't fall, I told her how to make one forherself. You can make one for yourself, too, and

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when you've made it, why it doesn't fall will be clearto you.

EXPERIMENT 44Materials: Fresh egg

Pin

Candle

Paper funnel

BB shot

With the pin puncture a small hole in both endsof an egg. Then blow hard in one hole, holding theother hole over a cup. This will force the contents

of the egg into the cup. Keep the holes as small asyou can and still get the contents of the egg out byblowing. It may take you a little while to do this.

When you have emptied the egg, fill one of theholes with wax from a lighted candle.

HoU

Contents

of egg

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FN I hole withcandle wax

Then fashion a small paper funnel to fit in theother hole and drop in the BB shot until the eggfeels fairly heavy when you pick it up.

Paperfunnel

BB shot

Candle wax

Then close the remaining hole with wax fromthe candle. Draw a face on the egg with a crayonand balance your Humpty Dumpty near the edge ofthe table.

You can see now why your Humpty Dumptypeers over the edge of the table without falling off.

Ordinarily the center of gravity of an egg is some-where in the middle of the yolk. When you took the

contents of the egg

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