1. Conservation of Energy

2. What are the two kinds of energy that we learned about thus far and how do we define them? Potential Energy – energy an object has due to its height Kinetic Energy – energy an object has due to its motion

3. If a 2 kg ball is held motionless 2 meters above the ground, what kind of energy does it have? About how much energy does it have? Potential Energy PE = mgh (2)(10)(2) = 40 J

4. If I drop the ball, does it increase or decrease in height? What happens to its potential energy? Decrease in height Potential Energy decreases

5. If I drop the ball, what happens to its speed? Does it increase or decrease? What happens to its kinetic energy? Speed increases Kinetic Energy increases

6. Halfway down, does the ball have potential energy? Why? Does the ball have kinetic energy? Why? The ball still has Potential Energy because it still has height above the ground The ball has Kinetic Energy because it is moving downward with a speed height velocity

7. What happens to the potential energy as the ball moves towards the ground? Potential Energy transforms into Kinetic Energy as the ball falls

8. Can an object gain extra energy if nothing acts on it? What about lose energy? An object cannot gain energy without being acted upon by an outside force An object also cannot lose energy without being acted upon by an outside force

9. What is the law of Conservation of Energy? Energy cannot be created nor destroyed. It can only be transformed into another kind of energy or transferred to another object

10. What other kinds of energy can potential or kinetic energy be transformed into? Heat Sound Light Chemical Electromagnetic Nuclear

11. Give some examples of energy transferred to another object? You give some examples…

12. If I drop this ball/pendulum, do you think it will come back and hit me? Why or why not? It does not hit me, because the pendulum cannot gain any extra energy unless acted upon

13. What would I need to do in order to get the pendulum to hit me? Someone would need to push on it Add extra energy to the ball by performing work on it

14. This mass floats motionless above the ground by a spring. What kind of energy does it currently have? How do you know? The mass has potential energy Because it has height above the floor

15. If I pull down on this mass, what do you think will happen to the mass once I let go? Why is that? The mass shoots upwards Because the spring pulls it up with a force

16. What would happen if I pull the object down farther before I let go? So one thing this force depends on would be? The mass would shoot up higher Distance from rest position – we’ll call it “x”

17. Now I’m going to switch to a different spring. What’s the difference between the two springs? The second spring is more rigid than the first This stiffness is known as the Spring Constant – we’ll call it “k”

18. What would happen if I pull the mass down to the same height as before? Why? The mass will shoot up higher The stiffness adds extra force Thus the spring constant and the force are directly proportional

19. So what does this Force (from the spring) depend on again? What would be our equation? We’re missing one thing though; if I pull downward on the mass, which way does the force pull? What are we missing? Distance from rest & spring constant F = kx The opposite direction A negative sign  F = -kx

20. If I push with a force of 50 N on a spring that has a spring constant of 25 N/m, how far does the spring move? F = kx 50 = 25(x) X = 50/25 = 2 m

21. If an object that has a weight of 300 N hangs on a spring and it moves 3 m, what is the spring constant of the spring? F = kx 300 = k (3) K = 300/3 = 100 N/m

22. If an object that has a mass of 10 kg hangs on a spring and it moves 2 m, what is the spring constant of the spring? F = kx F = mg mg = kx K = mg/x = 10(10)/2 = 50 N/m

23. If I pull down on the spring, will it do work once I let go? How do you know? The spring does do work The spring pulls the mass a certain distance with a force

24. If the spring can do work after being stretched, what must it have to do such work? What kind? What does it depend on? What is our equation? Energy! Potential Energy Distance from rest & spring constant PE s = ½ kx 2

25. Give some examples of other things that behave similar to springs: Gum Bands Bungie Cord String on a bow and arrow Slinky…everyone loves them!