1. 7 Energy

2. Work W = Fd (F parallel to d) W = 0 (F perpendicular to d)
Work is change in energy
Energy is the capacity to do work
Energy can be positional or motional

3. Energy
Positional Energy is called Potential Energy, e.g. stretched spring
Motional Energy is called Kinetic Energy
SI Units for Work and Energy: J = Nm = kgm2/s2

4. Work-Energy Theorem Work = D(KE)
Examples: Positional-Motional Energy Transformations:
Bow and Arrow Mass on Spring Inclined Plane

5. Conservation of Energy
Energy cannot be created or destroyed; it may be transformed (by work) from one form into another, but the total amount of energy never changes.
Energy Forms include: thermal, elastic, chemical, electromagnetic, nuclear, kinetic.

6. Machine
A device that changes an applied force by increasing it, decreasing it, or changes its direction.
Examples of Machines: pulley, lever, jack, inclined plane.

7. Efficiency
The percent of the work put into a machine that is converted into useful work output. efficiency = (work output)/(energy input)

8. Review Questions

9. 1. Front car 2. Middle car 3. Rear car 4. Other
In which car will you be moving the fastest at the very bottom of the incline?
This question can be restated: Where is the train when it has its maximum speed?
Which car will be at the bottom at this instant?
1. Front car 2. Middle car 3. Rear car 4. Other
Ch 7-3
Thanks to Joe Delaney.

10. 1. Front car 2. Middle car 3. Rear car 4. Other
The middle car is at the bottom when the train is moving the fastest.
1. Front car 2. Middle car 3. Rear car 4. Other
Ch 7-3
Thanks to Joe Delaney.
Answer: 2
The middle car. Of course, at any moment all cars have the same speed, but the gravitational potential energy of the system of cars is least when the middle car is at the bottom—when the center of mass of the system is lowest. Lowest potential energy means highest kinetic energy. So sit in the middle car for the fastest ride at the very bottom!