Other Physical Properties of Substances

By Moira Whitehouse PhD

•Some material floats in water and that is a physical property. Other material doesn’t float and that is also a physical property.

•Some substances are pulled by a magnet.

•Some substances are conductors of electricity (it can pass through them).

•Some substances are conductors of heat and others are not.

•These physical properties, as well as others, can be used to separate mixtures of substances.

some things float

and some things sink

Looking into this swimming pool we notice that there are “floaters” and their are “sinkers”.

You probably recognize that here we see one of each, a floater and a sinker.

One physical property of cork is that it floats in water.

Likewise, a physical property of this rock is that it sinks to the bottom in water.

If floating is a physical property of a substance, would any size or shape piece of that material also float?

To find out, we will cut the cork into little pieces....

The whole cork floats...

And so do the small pieces...

From this we can learn that the size or shape of an object does not change its physical property.

By the same token, size or shape of an object is not a physical property of that material.

What about other substances, would the size and shape of the substance make a difference?

How about pine wood pieces and sawdust from pine wood?

These tiny pieces of wood (saw dust) float too, until they soak up too much water and become heavy.

Could a liquid also have a physical property of floating on water?

Yes, we can clearly see that the cooking oil is floating on top of the water.

When oil tankers have accidents and spill their oil, the same thing happens, the oil floats....causing great problems for the environment because it is difficult to clean up.

Because oil floats on water, however, the oil can sometime be skimmed off of the water.

So, floating stuff on top of the water can be skimmed off....

And removed from the water.

Next, let’s look at some objects to see if they have the physical property of being attracted by a magnet. Such objects are called magnetic.

This is a bar magnet. It is almost touching a lolly-pop stick. The lolly-pop stick does not move because wood is not magnetic.

nickel.......magnetic

silver solder....... not magnetic

steel paper clips....... magnetic

steel drill bit....... magnetic

iron bolt....... magnetic

cardboard....... not magnetic

copper....... not magnetic

rubber....... not magnetic

zinc....... not magnetic

steel spoon....... magnetic

tin....... not magnetic

brass....... not magnetic

Aluminum foil......non magnetic

Knitting yarn......non magnetic

“tin can” actually made of steel......magnetic

What did you notice about all the stuff that was magnetic? Only metals are magnetic, but not all metals are magnetic. Only those metals things of iron/steel, nickel and cobalt are magnetic.

•However, nickel and cobalt are rare and expensive metals so we see very few things made of these substances.

The next physical property we will examine is the ability of a substance to conduct or pass an electric current. Those things that conduct electricity are called conductors and if they don’t conduct, they are called insulators.

To find out if a substance is a conductor we will use this device.

It sends battery power to the light bulb when there is a connection between the red and black wires.

This magnet is made of iron so it is a conductor and lets electricity pass through. Would the light on the tester be lit?

We will start with the silver solder.

It lets the current pass from the red to the black wire, and the light lights.

The current does not travel through wood. No light.

The current does not travel through rubber. No light.

The current passes through the nickel and lights the light.

The current passes through the zinc and lights the light.

The current does not travel through paper. No light.

The current does not travel through plastic. No light.

The current passes through the steel and lights the light.

The current passes through the tin and lights the light.

The current passes through the steel paper clips and lights the light.

The current passes through the aluminum foil and lights the light.

The current passes through the copper and lights the light.

The current does not pass through the knitting yarn. No light.

The current passes through the brass washers and lights the light.

We found that the following substances are conductors of electricity—that electrons go through them easily:•tin•aluminum•copper•brass•zinc•iron•silver

What do you notice about all items on this list of substances.

All these conductors are metals.

Next we will examine some substances that conduct something else, heat. You can probably think of some things used in the kitchen that need to be good conductors.

Sure, saucepans and other pans that we use to heat food have to be good conductors of heat in order for heat to travel from the stovetop or oven to the food.

aluminum

stainless steel

Copper lined with tin

cast iron

All these substances, aluminum, copper, tin and steel conduct heat. They are all____________.

With many modern saucepans you cannot see the metal the pan is made out of because they have a inner coating covering the metal that helps prevent food from sticking or a hard outer surface.

In addition to the metals, here are some other good conductors of heat?

Things that do not conduct heat are called insulators of heat—substances that do not allow heat to travel through them easily.

What substances do we use to stop heat from traveling to our hands when we cook?

Yes, cloth, plastic and wood are all poor conductors of heat. They are heat insulators.

Yes, cloth, plastic and wood are all poor conductors of heat. They are heat insulators.

What things do we wear or what do animals have to keep the heat from escaping from their bodies. These are all poor conductors of heat?

ebbie sonnberg at www.flickr.com nikon jim’s at www.flickr.com

dave winthrow at www.flickr.com

What insulates these animals—helps keep the heat inside their bodies?

We wear things like this to insulate our bodies from the cold?

A carpenter had dropped iron nails he was using to build a house into the sawdust, sand and small sticks around the building. How could he separate these substances?

To show how physical properties can be used to organize or separate things we will use the following:

Here is the mess he wants to separate..

The first thing he will do is get the nails out of the pile. How could he do that?

OK for the nails,, now he needs to separate the sand from the gravel and sticks. Any thoughts?

He used a sieve to separate the bigger stuff from the sand.

How can he separate the sticks from the gravel?

He poured the contents into a bowl of water.

The sticks floated to the top and the stones fell to the bottom.

Skim off the sticks.

Pour off the water and remaining is the clean gravel .

Isn’t it amazing what can be done with just a little knowledge about physical properties.