1. Ch 8 Energy Notes
Work
When the kinetic energy of an object changes, work has been done on the object.
Units of work: Joules
Work is a scalar quantity.

2. Work Work depends on: The amount of force applied to the object.
Ch 8 Energy Notes
Work
Work depends on:
The amount of force applied to the object.
The distance that the object moves while the force is applied.
The direction of the force with respect to the direction the object moves.

3. Ch 8 Energy Notes
Work
If the force on the object is in the direction the object moves, the work done is:
W = Fd F x

4. Ch 8 Energy Notes
Work
If the direction of the force is opposite the direction the object moves, work is:
W = -Fd F x

5. Ch 8 Energy Notes
Force is NOT Work
If the force is perpendicular to the direction the object moves, the work done is 0.
If the object doesn’t move, the work done is 0. F
W = 0 x

6. Work and Kinetic Energy
Ch 8 Energy Notes
Work and Kinetic Energy
The work done on an object by the net force equals the object’s change in kinetic energy.
Wnet = DKE

7. Power DWork Power = time W P t Power is the rate work is done.
Ch 8 Energy Notes
Power
Power is the rate work is done.
DWork
Power =
time W P t

8. Power Units of power: 1 Joule/sec = 1 Watt 1000 Watts = 1 kilowatt
Ch 8 Energy Notes
Power
Units of power: 1 Joule/sec = 1 Watt
1000 Watts = 1 kilowatt
Power is a scalar quantity.

9. (Simple) Machines A machine is a mechanical device used to do work.
Ch 8 Energy Notes
(Simple) Machines
A machine is a mechanical device used to do work.
Examples of simple machines:
Inclined plane
Lever
pulley

10. (Simple) Machines Workout = Workin
Ch 8 Energy Notes
(Simple) Machines
A machine can never output more work (energy) than is put into it.
At best,
Workout = Workin
Machine
Workout
Workin

11. Ch 8 Energy Notes
Mechanical Advantage
Machines can’t multiply work or energy, but they can multiply force. Mechanical advantage measures how much a machine multiplies force.
Force machine exerts
MA =
Force you exert

12. Efficiency Useful work done Efficiency = x 100% Energy input
Ch 8 Energy Notes
Efficiency
The efficiency of a machine tells how much of the energy (work) that goes into the machine actually does useful work.
It is usually expressed as a percent.
Useful work done
Efficiency =
x 100%
Energy input