Potential and Kinetic Energy

1. Potential and Kinetic Energy

2. What is ENERGY? • Energy is the ability to do work. • Everything around you has energy, but you notice it only when a change takes place. • Anytime a change occurs, energy is transferred from one object to another

3. Energy… • is NEVER created or destroyed! • can only be STORED or TRANSFERRED.

4. For example, a bowling ball rolls down the alley and knocks down some pins. Is energy involved? • Yes! Kinetic energy. • A change occurs when the pins fall over. The bowling ball causes this change, so the bowling ball has energy. • What if the bowling ball is not moving? Does it still have energy? • Yes! Potential energy.

5. How is all energy divided? All Energy Potential Energy (PE) Kinetic Energy (KE)

6. Potential Energy is… • The energy stored in an object because of its position. • It has the “potential” to cause change.

7. Examples of Potential Energy: A stretched rubber band.. Water at the top of a waterfall.. A drawn Bow and Arrow… Yo–Yo held in your hand..

8. The higher an object, the more potential energy. • The more mass an object has, the more potential energy it has ….because it has the “potential” to cause more change.

9. Calculating PE

10. Examples • There is a bell at the top of a tower that is 45 m high. The bell weighs 190 kg. What is its potential energy? PE = mgh PE = (190 kg)(9.8 m/s2)(45 m) PE = 83790 Joules PE = 8.4 x 104 J

11. 2. A box has a mass of 5.8 kg. The box is lifted from the garage floor and put on a shelf. If the box gains 145 J of potential energy, how high is the shelf? PE = mgh 145 J = (5.8 kg) (9.8 m/s2) h 145 = 56.84h 56.84 56.84 2.55 m = h 2.6 m = h

12. 3. A 800 g ball is pulled up a slope as shown in the diagram. Calculate the potential energy it gains. PE = mgh PE = (0.8 kg)(9.8m/s2)(0.2m) PE = 1.568 J PE = 1.6 J

13. Potential Energy Converted to Kinetic Energy… • When stored energy begins to move, the object now transfers from potential energy into kinetic energy.

14. Kinetic Energy Is… • The energy of a moving object. • "Kinetic" means movement. • When stored energy is being used up, it is making things move or happen. • If an object isn’t moving, it doesn’t have kinetic energy.

15. Kinetic energy increases as an object moves faster. • For example: If you roll the bowling ball so it moves faster, what happens when it hits the pins? • A faster ball causes more change to occur than a slower ball so it has more KE

16. The heavier the object, the more kinetic energy is produced. • For example: If a volleyball travelling at the same speed as a bowling ball is sent down the alley, does it will send pins flying as far? • No! Even though the volleyball is moving at the same speed, it has less kinetic energy because is has less mass.

17. Calculating KE

18. Examples • A car is traveling with a velocity of 40.0 m/s and has a mass of 1120 kg. Calculate its kinetic energy. KE = ½ mv2 = 0.5 (1120 kg)(40 m/s)2 = 896000 J = 8.96 x 103 J

19. 2. A golf pro swings his driver which weighs 750 g at a velocity of 60.0 m/s. Calculate the kinetic energy of the club. KE = ½ mv2 KE = (0.5)(0.75 kg)(60.0 m/s) 2 = 1350 J = 1.4 x 103 J

20. 3. If a soccer ball has 40 J of kinetic energy and weighs 800 g, what velocity was it kicked at? KE = ½ mv2 40 = (0.5)(0.8 kg) v2 40 = 0.4v2 0.4 0.4 100 = v2 10 = v

21. An object has the MOST kinetic energy when it’s movement is the GREATEST. • When an object has the LEAST potential energy, it has the MOST kinetic energy. • Animated Roller Coaster