1. Work, Power and Conservation of Energy

2. Work An applied force acting through a distance parallel to the force
Units of work (and energy) = joule (J)
Zero distance, no work
Displacement perpendicular to applied force, no work

3. Power The rate at which work is done Units: watts (W), horsepower (hp)
Example: Walking versus running upstairs
The “power bill” - you pay for energy

4. Motion, position and energy
Work and energy related
Energy = ability to do work
Work = process of changing energy

5. Energy Pie Charts
The size of the circle indicates how much total energy is present – a closed system (no energy flow in or out of the system) would have the same size circle/pie
If energy has been added to the system, we would draw a larger “pie” graph than before
If energy has been removed from the system, we would draw a smaller “pie” graph than before

6. Energy Pie Charts
Energy that stays in the system sometimes becomes thermal energy or internal energy – Etherm or Eint
Internal Energy – energy used to rearrange the internal structure of an object
Thermal Energy – energy of the motion of the particles of an object

7. A ball is held above the ground, and then is dropped so it falls straight down. (Restrict your analysis to the ball moving in the air, BEFORE it hits the ground.) EG EG EK EG EK EG
ETh EK
EIh EK

8. A Popper and Pie Charts C B D A E

9. Energy Bar Graphs
Energy Bar Graphs can be used to show energy transformations as well
Bar graphs can provide a more quantitative view of the system’s energy transformations
They can also be used to show energy transfers into or out of a system (eventually)

11. Energy Bar Graphs