1. Chapter 5
Work and energy

2. Introduction Energy present in many forms in universe
Mechanical, chemical, electromagnetic, nuclear
The total energy in the universe remains constant…Law of conservation of energy
Energy can only change forms, can’t be created or destroyed
Work is the link between concept of froce and energy

3. 5.1 Work
Work occurs when a force is applied to an object over a distance and the object moves
It must move in the direction of the applied force
It must move

4. 5.1 Work Work is a scalar quantity Units are joules: Newton-meter
Work makes you “mad”

5. 5.2 Kinetic Energy Kinetic Energy: energy of motion
Has same units as work (joules)

6. 5.2 Kinetic Energy Known as the “work energy theorem”
Work done on an object is equal to change in its kinetic energy
If positive, work goes into the system
If negative, work comes out of the system

7. 5.3 Potential Energy Potential energy is the energy of “position”
Aka Gravitational Potential energy
Same units as work…joules

8. 5.4 Conservative and Nonconservative Forces
Conservative forces: the work done on an object does not depend on the path
E.g. the force of gravity
Nonconservative forces lead to lost energy
E.g Friction

9. 5.5 Conservation of Mechanical Energy
When a physical quantity is conserved, the value of the quantity remains constant
If objects are effected only by conservative forces, then total mechanical energy will remain constant

10. 5.5 Conservation of Mechanical Energy
Hook’s Law describes the energy stored in a spring
Elastic Potential energy

11. 5.6 Nonconservative Forces
The work done by all nonconservative forces is equal to the change in mechanical energy

12. 5.8 Power Power is the time rate of doing work
If work makes you “mad”, power is “how long” you are mad
Measured in “watts”