Measurements
August 24, 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 miles
o 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 of
o The sun is 150 billion m away has words in it, so you can’t do math
o 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?
6th and 7th grade
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
x1
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
8th grade
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
dekameter
x1
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
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 version
o 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 units
o Energy = Joules = J = N/m2 = 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
Length
Length: 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
Time
Time: 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!
Mass
Mass: 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!
Temperature
Temperature: 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 = L
o How much 3D space something takes up
o 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 solid
o 1 g/mL = 1 g/cm3, so they’re really the same thing
o Example of “mixing and matching” SI units to make a new
measurement
Volume
Volume: 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
stumpy
o 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
Density
Density: 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 it
o He stepped into a bath and it overflowed – displaced
volume
o We still use his method
Questions
• Any questions about the slides?
• Any new questions?
Old Questions
• What is the most dangerous big cat?
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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?