1. Conservation of Energy

2. How many different energy types can you name
How many different energy types can you name? How many different energy transformations can you identify?

3. Demo: Does a Book Have Energy?
Discussion Questions
What kind of energy does the book have when it was lying on the stool?
Does the book have any energy lying on the table top?
What type of energy did the book impart to the metre stick?
What kind of energy did the eraser attain?

4. Law of Conservation of Energy
The total amount of energy in the universe is conserved.
Energy cannot be created out of nothing, and existing energy cannot just disappear: energy can only change forms.
During an energy transformation, the total amount of energy remains constant.

5. Conservation of Mechanical Energy

6. Conservation Conceptual Questions
How does the car’s total mechanical energy, kinetic energy, and gravitational potential energy compare A, B and C? A C B

7. Conservation Conceptual Question
The masses of the cars in the picture below are identical. All four cars are released from rest simultaneously from point A. Which car is travelling the fastest by point B?

8. Law of Conservation of Energy
Total mechanical energy is conserved (so long as no work is done by other forces):
ET = ET’
Eg + Ek = Eg’ + Ek’
ET = total mechanical energy (J)
Eg = gravitational potential energy (J)
Ek = kinetic energy (J)

10. Example Problem
An astronaut on the moon stands on a cliff and drops a 20 kg rock from a height of 30 m. (gMoon = 1.6 N/kg)
a) What is the rock’s KE at the top of the cliff?
What is the rock’s GPE at the bottom of the cliff?
b) Use the bottom of the cliff as the reference point.
i. What is the rock’s ET just before it is dropped?
ii. What is the rock’s KE and velocity at the bottom of the cliff?
c) What is the rock’s velocity 10 m from the bottom?
Try Pg. 241 Practice Question #1

11. Homework
Pg. 235 #2, 5
Pg. 241#1, 2, 3

12. Demo: Will the Brick Hit Your Nose?
Discussion Questions
Will the pendulum ever swing higher than its initial position?
What would give the brick a higher swing?
What forms of energy are involved in a swinging pendulum?
Are these energies constant? If not, where does the energy go? What does it turn into?
In which positions does the pendulum have the greatest kinetic energy? Potential energy?
Video 1, Video 2

13. Demo: Will the Brick Hit Your Nose?

14. Conservation of Mechanical Energy

16. Conservation of Mechanical Energy