1. Conservation of Energy IT’S THE LAW

2. Lifting a Ball When you lift a ball to a certain height you do work on it. When you lift a ball to a certain height you do work on it. This work (W) is equal to the weight of the ball (w=mg) times the height (h). This work (W) is equal to the weight of the ball (w=mg) times the height (h). The work done to lift the ball is stored as potential energy. The work done to lift the ball is stored as potential energy. h W = Fd =wh = mgh PE = W = mgh

3. Lifting a Ball The ball now has potential energy stored in it. The ball now has potential energy stored in it. This means the ball has the potential to do work if you drop it on something. This means the ball has the potential to do work if you drop it on something. But before it can do that work it must convert the PE to another form of energy called kinetic energy – energy of motion But before it can do that work it must convert the PE to another form of energy called kinetic energy – energy of motion h PE = mgh Kinetic Energy Energy of Motion

4. Kinetic Energy Kinetic Energy (KE) is energy of motion. Kinetic Energy (KE) is energy of motion. Kinetic Energy depends on the moving object’s mass (m) and the square of its speed (v). Kinetic Energy depends on the moving object’s mass (m) and the square of its speed (v).

5. Lifting a Ball As the ball falls: Its Potential Energy decreases because its height decreases. Its Potential Energy decreases because its height decreases. Its Kinetic Energy increases because it speeds up. Its Kinetic Energy increases because it speeds up. It turns out the amount of potential energy lost as the ball falls is the same as the amount of kinetic energy the ball gains!!!! It turns out the amount of potential energy lost as the ball falls is the same as the amount of kinetic energy the ball gains!!!! h PE = mgh Kinetic Energy Energy of Motion

6. The Law of Conservation of Energy Energy cannot be created nor destroyed, it can just be transformed from one form to another, or transferred from one object to another. If we ignore any losses in energy to sound or heat (two big sources) this means that PE + KE will always remain constant.

7. The sum of all the potential energy and the kinetic energy of a system is defined as its mechanical energy. In an isolated, closed system, if there are no losses in energy in the form of sound or heat, then the mechanical energy of a system is conserved.

8. A Falling Ball A 2-kg ball falls from a height of 5-m. Trace its PE & KE as it falls. 5-m HeightPE=mghKEME 5-m 4-m 3-m 2-m 1-m 0-m 100-J 0-J 100-J 100-J 100-J 100-J 100-J 100-J PE = (2)(10)(5) =100-J Since the ball isn’t moving, KE = 0-J!!!! PE + KE = 100 + 0 = 100-J Conservation of Energy says ME will always be 100-J the entire time the ball falls!!!!!

9. A Falling Ball A 2-kg ball falls from a height of 5-m. Trace its PE & KE as it falls. 4-m HeightPE=mghKEME 5-m 4-m 3-m 2-m 1-m 0-m 100-J 0-J 100-J 100-J 80-J 20-J PE = (2)(10)(4) =80-J KE = 100 – 80 = 20-J 100-J 100-J 100-J 100-J

10. A Falling Ball A 2-kg ball falls from a height of 5-m. Trace its PE & KE as it falls. 3-m HeightPE=mghKEME 5-m 4-m 3-m 2-m 1-m 0-m 100-J 0-J 100-J 100-J 80-J 20-J PE = (2)(10)(3) =60-J KE = 100 – 60 = 40-J 100-J 100-J 100-J 100-J 40-J 60-J

11. A Falling Ball A 2-kg ball falls from a height of 5-m. Trace its PE & KE as it falls. 2-m HeightPE=mghKEME 5-m 4-m 3-m 2-m 1-m 0-m 100-J 0-J 100-J 100-J 80-J 20-J PE = (2)(10)(2) =40-J KE = 100 – 40 = 60-J 100-J 100-J 100-J 100-J 40-J 60-J 40-J 60-J

12. A Falling Ball A 2-kg ball falls from a height of 5-m. Trace its PE & KE as it falls. 1-m HeightPE=mghKEME 5-m 4-m 3-m 2-m 1-m 0-m 100-J 0-J 100-J 100-J 80-J 20-J PE = (2)(10)(1) =20-J KE = 100 – 20 = 80-J 100-J 100-J 100-J 100-J 40-J 60-J 40-J 60-J 20-J 80-J

13. A Falling Ball A 2-kg ball falls from a height of 5-m. Trace its PE & KE as it falls. HeightPE=mghKEME 5-m 4-m 3-m 2-m 1-m 0-m 100-J 0-J 100-J 100-J 80-J 20-J PE = (2)(10)(0) =0-J KE = 100 –0 = 100-J 100-J 100-J 100-J 100-J 40-J 60-J 40-J 60-J 20-J 80-J 0-J 100-J

14. A Falling Ball A 2-kg ball falls from a height of 5-m. Trace its PE & KE as it falls. HeightPE=mghKEME 5-m 4-m 3-m 2-m 1-m 0-m 100-J 0-J 100-J 100-J 80-J 20-J 100-J 100-J 100-J 100-J 40-J 60-J 40-J 60-J 20-J 80-J 0-J 100-J Where does the ball have its maximum speed? Just before it hits the ground --- WHERE ITS KE IS LARGEST

15. A Falling Ball A 2-kg ball falls from a height of 5-m. Trace its PE & KE as it falls. HeightPE=mghKEME 5-m 4-m 3-m 2-m 1-m 0-m 100-J 0-J 100-J 100-J 80-J 20-J 100-J 100-J 100-J 100-J 40-J 60-J 40-J 60-J 20-J 80-J 0-J 100-J If the ball bounces back up, what height will it reach? Since it only has 100-J available, it will only reach its original height of 5-m!!!!

16. A Falling Ball A 2-kg ball falls from a height of 5-m. Trace its PE & KE as it falls. HeightPE=mghKEME 5-m 4-m 3-m 2-m 1-m 0-m 100-J 0-J 100-J 100-J 80-J 20-J 100-J 100-J 100-J 100-J 40-J 60-J 40-J 60-J 20-J 80-J 0-J 100-J If the ball loses 20-J to heat (air resistance) and sound, how high will it bounce? Since it only has 80-J (100 – 20) available, it will only reach a height of 4-m!!!!

17. Pendulums & Roller Coasters Pendulums and Roller Coasters must follow the Law of Conservation of Energy Pendulums and Roller Coasters must follow the Law of Conservation of Energy IT’S THE LAW IT’S THE LAW This means that what ever potential energy is stored in each at the beginning is transferred back and forth between PE & KE. This means that what ever potential energy is stored in each at the beginning is transferred back and forth between PE & KE. If we are allowing for losses in energy from heat and sound, then this amount of energy slowly disappears. If we are allowing for losses in energy from heat and sound, then this amount of energy slowly disappears.

18. A Pendulum PE KE

19. A Pendulum If there are losses in energy to heat and sound, then the height it reaches each swing gets lower and lower until it stops swinging.

20. Roller Coasters Roller Coasters use the potential energy stored when it is at the top of a hill and converts it to kinetic energy throughout the ride. Roller Coasters use the potential energy stored when it is at the top of a hill and converts it to kinetic energy throughout the ride. WEeeeeeeeee!!!!!!!!! WEeeeeeeeee!!!!!!!!!