1. Chapter 9
Section 4 – pg 358
Energy

2. Energy: the ability to do work or cause change (measured in joules)
Pg 358
Work: an object is caused to move a certain distance; the transfer of energy (measured in joules)
Energy: the ability to do work or cause change (measured in joules)
A pitcher does work on a ball when pitching – energy is transferred to the ball from the pitch

3. Pg 359
Kinetic Energy
Kinetic Energy: the energy an object has due to its motion
kinetos Greek for “moving”
The kinetic energy of an object depends on both its mass and its speed
Kinetic energy increases when mass increases
This is why a bowling ball dropped on your toes hurts more than a tennis ball
Kinetic energy also increases when speed increases
A fast traveling bowling ball will knock down more pins than a slow one

4. Kinetic Energy = ½ x Mass x Speed2
Pg 359
Kinetic Energy = ½ x Mass x Speed2
Note that changing the speed of the object will have a greater effect on its kinetic energy than changing its mass by the same factor

5. Pg 360
Potential Energy
Some objects have stored energy as a result of their positions or shapes
Potential Energy: stored energy that results from the position or shape of an object
This type of energy has the potential to do work

6. Gravitational Potential Energy
Pg 360
Gravitational Potential Energy
Gravitational Potential Energy: potential energy related to an object’s height
An object’s gravitational potential energy depends on its weight and on its height relative to a reference point
Gravitational Potential Energy = Weight x Height

7. Elastic Potential Energy
Pg 360
Elastic Potential Energy
Elastic Potential Energy: the potential energy of objects that can be stretched or compressed

8. Energy Transformation and Conservation
Pg 361
Energy Transformation and Conservation
Mechanical Energy: an object’s combined kinetic energy and potential energy
Mechanical Energy = Kinetic energy + Potential energy
A ball thrown into the air has both kinetic (from its motion) and potential (from its height) energy

9. Transformations Between Potential and Kinetic Energy
One of the most common energy transformations is the transformation between potential energy and kinetic energy
Any object that rises or falls experiences a change in its kinetic and gravitational potential energy
In a pendulum, a continuous
transformation between kinetic and
potential energy takes place
Pg 362

10. Conservation of Energy
Pg 363
Conservation of Energy
The law of conservation of energy states that when one form of energy is transformed to another, no energy is destroyed in the process
According to the law of
conservation of energy, energy can
not be created or destroyed
If you add up all the new forms of
energy after a transformation, all
of the original energy will be
accounted for

11. Chapter 9 Section 4 Homework – pg 363

12. 1A. What is kinetic energy? In what unit is it measured?

13. 1B. What factors affect an object’s kinetic energy?

14. 1C. A 1,500-kg car is moving at a speed of 10 m/s
1C. A 1,500-kg car is moving at a speed of 10 m/s. What is the car’s kinetic energy?

15. 2A. What is potential energy?

16. 2B. What factors affect an object’s gravitational potential energy?

17. 2C. What is the potential energy of a 500-N pole-vaulter when she is 4 m above the ground?

18. 3A. State the law of conservation of energy in your own words

19. 3B. Describe the energy transformations that occur when you bounce a ball

20. 3C. Suppose a ball had a potential energy of 5 J when you dropped it
3C. Suppose a ball had a potential energy of 5 J when you dropped it. What would be its kinetic energy just as it hit the ground?