Journal 2/2/16
Why is it important to have units? Why do we need to have a
way to measure different things?
Objective
Tonight’s Homework
To learn what it means
when we combine units
none
Getting Familiar with Units
Physics has a lot of units. The way we measure things.
Some of the make sense
Velocity = Distance covered / time it took  meters / second
Water pressure = flow rate ● how much resistance
Rocket = Energy to go up / weight  joules / kilogram
But we can certainly have stranger combinations:
Kilograms / meter3 / kilogram = Density / mass
This unit might explain how something gets more dense as you
pack more stuff on. Jupiter works this way!
Getting Familiar with Units
So what do we do with this?
Each of you is going to collect a small packet of terms. These
have the most basic units on them. Mr. C. wants you to find
ways of combining these to get the effects described. Then
you’re going to combine units and describe to me what that
might represent.
Example 1:
Something pushes harder the hotter it gets
Newtons / °C
Example 2:
Create something to go with joules / meter2
This might describe how much energy can be stored on the
surface of a sheet of metal.
Getting Familiar with Units
Let’s look at the basic units you’ll be getting.
°C
- measures temperature
Joules
- measures energy (any type)
Meters
- measures distance
Kilograms
- measures weight or mass
Seconds
- measures time
Newtons
- measures force
Candelas
- measures brightness
Coulombs
- measures electrical charge
If we divide units, we’re comparing them. Usually either “how much of the
top does it take to change the bottom by 1?” OR “how many of the top can
happen each time the bottom goes up by 1?”
If we multiply units, we’re saying that both have an effect. Usually “If I
double A or B, my result doubles!”
Squared units are usually used for areas, cubed units for volumes.
Getting Familiar with Units
So let’s get to it. Work in pairs to create units for…
1) The amount of light each chunk of material can make.
2) How temperature drops as you get closer to a glacier.
3) How much space a space heater can provide heat for.
4) The amount of electricity a power plant makes in a day.
5) How much force something has if its both heavy and fast.
6) How much energy you could generate if an exercise bike
was hooked up to a generator.
Getting Familiar with Units
Come up with a situation for each of the unit combos
1) Candelas / Coulomb
2) Kilograms / °C
3) Meters / Newton
4) Coulombs / Candela / Meters2
5) Joules / Meters2 / Second
6) Joules / kilograms / Second
Exit Question
What units would go with this?
Measuring how much energy is contained in a piece of
coal.
a) Coulombs / Kilograms
b) Kilograms / Coulombs
c) Kilograms / Joules
d) Joules / Kilograms
e) Any of the above
f) None of the above