Measurements

September 15, 2015(2.1 in your books)

Meme Moment

Scientist of the Day

Margaret Hamilton• Started off as a teacher (math

& French)• Went back to grad school to

learn about programming before it was even a thing

• Computer programmer for Apollo 11 mission

• Software design still used today• Made sure moon landing

happened• Entrepreneur

Metric System• Replaced weird measurements like “hands” or “cubits”

that vary from place to place, as well as mileso A cubit is the length of your fingertip to your elbow

• Based around water, which is the same everywhere• 1 g of water = 1 cm3 = 1 mL (at 4ºC)• Once you have a unit, you can add a prefix to save

space.o The sun is 150,000,000,000 m away has a lot of 0s to keep

track ofo The sun is 150 billion m away has words in it, so you can’t do

matho The sun is 150 Gm away(gigameters)

Imperial vs Metric

Measurement Imperial Metric

length inches, feet, yards, miles, leagues meter

volume ounces, pints, quarts, gallons liter

mass grains, pounds, stones, slugs gram

Who doesn’t use the metric system?

Prefixes

Symbol Prefix Math 10n Example

k kilo x 1000 x 103 kilogram

h hecto x 100 x 102 hectometer

da deka x 10 x 101 dekaliter

x 1 x 100 liter

d deci x 0.1 x 10-1 decimeter

c centi x 0.01 x 10-2 centimeter

m milli x 0.001 x 10-3 milligram

Different ways of writing the same

thing

6th and 7th grade

PrefixesSymbol Prefix Math 10n Example

k kilo x 1000 x 103 kilogram

h hecto x 100 x 102 hectometer

da deka x 10 x 101 dekameter

x 1 x 100 liter

d deci x 0.1 x 10-1 decimeter

c centi x 0.01 x 10-2 centimeter

m milli x 0.001 x 10-3 milligram

µ micro x 0.000001 x 10-6 microliter

n nano x 0.000000001 x 10-9 nanogram

Different ways of writing the same

thing

8th grade

SI Units• Fancier version of the metric system• “International system of units”

o The acronym doesn’t match because it’s international. o Acronym comes from the French versiono Système International d'Unités

• 7 base quantities – if you know these, you can describe any quantitative measurement.

• Everything we know for certain is based on those 7 types of numbers

• We’ll use other units/descriptions/symbols like “energy” or “density” or “power,” but we can always trace them back to SI unitso Energy = Joules = J = N·m = kg·m2/s2

SI Units

• K = Kelvin = temperature• s = second = time• m = meter = length• kg = mass = how heavy

(ish)• cd = candela = how bright• mol = mole = amount of

stuff• A = ampere = electric

current

LengthLength: distance from one point to another

• SI unit = meter = m

Estimating:• 1 m ≈ 1 yard = 3 feet• 1 cm ≈ the width of your finger• 1 km ≈ 0.6 miles

TimeTime: the period between 2 events

• SI unit = second = s

• Sometimes scientists get lazy and say “hours” or “days” instead of “____ kiloseconds”

• Milliseconds, etc are really popular in sports though!

MassMass: the amount of matter in an object

• Not the same as weight!• SI unit = kilogram = kg

Weight: the pull of gravity on an object. Mass and weight only match on earth.

• In space, objects have 0 weight. • A 5 kg object on earth still has 5 kg mass in space

– just have to measure it differently!

TemperatureTemperature: energy of molecules moving

• Molecules are always moving!• Lots of moving = high temperature, hot• Almost still = low temperature, cold

• SI unit = Kelvin = K• Metric system also uses Celsius = ºC

• K = 273 + ºC

Temperature Scales

Breaking Down SI Units

• Common measurements like “volume” and “density” don’t have their own SI unit, but we can still trace their metric system name to an SI unit

• Volume = liter = Lo How much 3D space something takes upo Everything is based on water, so 1 mL = 1 cm3

o Going back to SI units, 1 L = 0.001 m3 = 1 dm3

• Density is commonly g/mL or g/cm3

o Depends if you’re talking about liquid or solido 1 g/mL = 1 g/cm3, so they’re really the same thingo Example of “mixing and matching” SI units to make a

new measurement

VolumeVolume: Measures 3D space. Metric unit is liters (L). SI unit is cubic meters (m3).

• Often use milliliters also (mL)

Estimating:• 1 coke can ≈ 350 mL• 1 cup (for baking) ≈ 250 mL• 1 gallon of milk ≈ 4 L

Measuring Volume• Taller/longer is better than

stumpyo Easier to see the

measurements

• Measure at eye level• Real number is at the

bottom of the meniscus (the dip)o Water has a big meniscus

because of adhesion – it likes to stick to other things!

o Glass and mercury have an upside-down meniscus

DensityDensity: how much mass is in a given volume. SI unit = kg/m3

• Combines mass and volume.• Common metric measurements are g/mL and g/cm3

• Things float if they are less dense than the liquid• Things sink if they are more dense• When things are the same substance, they always

have the same density. o Water is always 1 g/mL (at 4ºC)

Density Formula

Density Formula

*just like we love comic sans. Not.

Eureka!• Archimedes was asked to figure out if a crown

was made of real gold and if it was all the gold the king had given to the jeweler. o It weighed the right amount, but what if another metal

had been added to make up the difference?o He couldn’t do the normal tests because that would

break the crown

• He yelled “Eureka!” when he figured out he could use density to test ito He stepped into a bath and it overflowed – displaced

volumeo We still use his method

Unit Conversions1. Find the conversion factor.

1 km = 1000 m2. Write it as a fraction (2 ways to do this).

3. You want the same unit on the top and the bottom.

Reminders• 8th grade Scientist of the

Day presentations begin Monday

• Only presentation part• Need 2 pictures• Half a slide of bullet point

facts• Tell people if they’re right

or wrong about subjective, qualitative, etc

• Turn it into a 2-minute story

8th grade

Questions• Any questions about the slides?

• Any new questions?

Old Questions• What is the most dangerous big cat?

• What is the most dangerous fish apart from sharks?

• What kinds of water snakes are venomous?• Where is West Nile virus and what does it do?• Picture of largest snake?• How many scientific laws are there?• What is fugacity?• How do spitting cobras work?