Equation Cheat Sheet
(Not “notes” but you will be writing some stuff down)
Instructions
• Take your white piece of paper and quarter it (fold or draw lines)
Force reminder
• Force is what causes movement (specifically it causes acceleration)
• Force is measured in “newtons” (N) after the famous Sir Isaac Newton
Work
• Work in physics is a measure of force applied over a distance
• Its unit is Joules (J), which is the
same as newtons times meters
• If something doesn’t move no
work is done
As hard as he pushes, if the wall
doesn’t move he didn’t do any work
Cheat Sheet
• In the upper left corner rectangle write “Work”
• Fill in the corner as follows:
Work
•
•
•
Work = (Force) x (Distance)
Units: Joules (J)
Same as N x m
Work is only performed if something
moves
Example problems:
• If you push a box with 60N of force over a distance of 3 meters, how
much work did you do?
Example problems:
• If you push a box with 60N of force over a distance of 3 meters, how
much work did you do?
1. Work = (Force) x (Distance)
2. Work = (60N) x (3m)
3. Work = 180 J
Example problems:
• If you did 40 joules of work to a box over 4 meters. How much force
did you push it with?
Example problems:
• If you did 40 joules of work to a box over 4 meters. How much force
did you push it with?
1.
2.
3.
4.
Work = (Force) x (Distance)
40J = (Force) x 4m
40J / 4m = (Force)
Force = 10N
Power
• Power in physics is a measure of how much work is being done in a
given time frame
• Its unit is Watts (W), which is the
same as joules divided by seconds
A 60 watt bulb is capable of handling
a certain amount of energy per time
without overheating
Cheat Sheet
• In the upper right corner rectangle write “Power”
• Fill in the corner as follows:
Power
•
•
•
Power = (Work) / (Time)
Units: Watts (W)
Same as J / s
Power is the rate at which work is
done.
Example problems:
• What was your power output if you did 50 joules of work in 10
seconds?
Example problems:
• What was your power output if you did 50 joules of work in 10
seconds?
1. Power = (Work) / (Time)
2. Power = 50J / 10s
3. Power = 5 W
Example problems:
• How long did it take you to do 15 joules of work if your power output
was 5 watts?
Example problems:
• How long did it take you to do 15 joules of work if your power output
was 5 watts?
1. Power = (Work) / (Time)
2. 5W = 15J / Time
3. Time = 15J / 5W = 3s
Example problems:
• What was your power output if you pushed a box 10 meters in 4
seconds with 2 newtons of force?
Example problems:
• What was your power output if you pushed a box 10 meters in 4
seconds with 2 newtons of force?
1.
2.
3.
4.
Work = (Force) x (Distance)
Work = 2N x 10m = 20J
Power = (Work) / (Time)
Power = 20J / 4s = 5 watts
Cheat Sheet
• In the bottom left corner rectangle write “Mechanical Advantage
(MA)”
• Fill in the corner as follows:
Mechanical Advantage (MA)
•
•
MA = (Output force) / (Input force)
Units: None
•
For levers: (Length of effort arm) / (length of
load arm)
Leave space for future notes
Example problems:
• What is the mechanical advantage of a lever if it has an input force of
15N and an output force of 60N?
Example problems:
• What is the mechanical advantage of a lever if it has an input force of
15N and an output force of 60N?
1. MA = (Output force) / (Input force)
2. MA = (60N) / (15N)
3. MA = 4
MA has no units
Example problems:
• What is the output force of a lever with a mechanical advantage of 3
if pressed on with 31N of force?
Example problems:
• What is the output force of a lever with a mechanical advantage of 3
if pressed on with 31N of force?
1. MA = (Output Force) / (Input Force)
2. 3 = (Output Force) / (31N)
3. 3 x 31N = Output Force = 93N
Force has units
Example problems:
• How long is the effort arm of a lever if it has a MA of 2.5 and a load
(resistance) arm length of 5cm?
Example problems:
• How long is the effort arm of a lever if it has a MA of 2.5 and a load
(resistance) arm length of 5cm?
1. MA = (Effort arm length) / (Load arm length)
2. 2.5 = (Effort arm length) / (5cm)
3. 2.5 x 5cm = Effort arm length = 12.5cm
Cheat Sheet
• In the bottom right corner rectangle write “Efficiency”
• Fill in the corner as follows:
Efficiency
•
•
Efficiency = (Output work) / (Input work)
Units: None
It is impossible to have an efficiency greater
than 1.
Example problems:
• What is the efficiency of a simple machine if you exert 200 J of work
and it produces 150 J as a result?
Example problems:
• What is the efficiency of a simple machine if you exert 200 J of work
and it produces 150 J as a result?
1. Efficiency = (Output work) / (Input work)
2. Efficiency = (150J) / (200J)
3. Efficiency = ¾ or 0.75
Efficiency has no units
Efficiency
• Why is it not possible to have an efficiency greater than 1?
Efficiency
• Why is it not possible to have an efficiency greater than 1?
• Because some energy is always used to overcome gravity and friction
Perpetual Motion Machine
• A “perpetual motion machine” is a theoretical device which has an
efficiency of 1, and therefore never stops
Perpetual Motion Machines
• People have tried to get “free energy” for many years with
contraptions such as these
Perpetual Motion Machines