Law of Conservation Of Energy

1. Law of Conservation Of Energy GLE 0607.10.3 Explain the principles underlying the Law of Conservation of Energy

2. The Law of Conservation of Energy • Gobble down five bananas and you'll have enough energy to swim for about an hour. That's because your body is a complex machine capable of turning one kind of energy (food) into another kind (movement).

3. Cars can pull off the same trick. Depending on which make and model you own, you probably know that it goes so many kilometers or miles to the gallon; in other words, using a certain amount of energy-rich gasoline, it can transport you (and a moderate load) a certain distance down the road.

4. What we have here are two examples of machines—the human body and the automobile—that obey one of the most important laws of physics: the conservation of energy.

5. Written in its simplest form, it says that you can't create or destroy energy, but you can convert it from one form into another. Pretty much everything that happens in the universe obeys this fundamental law.

6. Check for Understanding • Your body is a complex machine capable of turning one kind of _________ (food) into another kind (movement). • Cars use energy-rich ________ to transport (move) you a certain distance down the road. • Energy __________ be created or destroyed. • Energy can only be __________ into other forms of energy.

7. Answers • Energy • Gasoline • Can’t • Transformed

8. Music Video Clip • https://www.youtube.com/watch?v=bMz86CQsGug

9. Check for Understanding • Summarize the Law of Conservation of Energy.

10. Answer • In a closed system, energy can not be created or destroyed only transformed into a new form of energy.

11. Important Distinction • The first thing we need to note is that the law of conservation of energy is completely different from energy conservation. • Energy conservation means saving energy through such things as insulating your home or using public transportation; generally it saves you money and helps the planet. • The conservation of energy has nothing to do with saving energy: it's all about where energy comes from and where it goes.

12. Check for Understanding • How is the law of conservation of energy different from energy conservation?

13. Answers • Energy conservation means saving energy while the law of conservation of energy means that no energy is lost during energy transformations

14. Video Clip • https://www.youtube.com/watch?v=8GLtFNaiMH8

15. Real World Example • In the everyday world, "work" is something you do to earn money; in physics, work has a different meaning. When you do a useful job with a force (a push or a pull), such as moving a car uphill, we say you're doing work, and that takes energy. • If you push a car uphill, it has more potential energy at the top of the hill than it had at the bottom. Have you violated the conservation of energy by creating potential energy out of thin air?

16. No! To push the car, you have to do work against the force of gravity. Your body has to use energy to do work. Most of the energy your body uses is gained by the car as you push it uphill. The energy your body loses is pretty much equal to the work it does against gravity. And the energy the car gains is the same as the work done. • So no energy is created or destroyed here: you're simply converting energy stored as fuel inside your body into potential energy stored by the car (because of its height).

17. Check for Understanding • What is the physics definition of work? • Does the car have more or less potential energy at the top of the hill compared to what it had at the bottom? • When you push the car uphill, you work against what? • The energy you use to push the car uphill is transformed into what kind of energy?

18. Answers • Work is using force to do something. • The car has more potential energy at the top of the hill than it had at the bottom. • To push the car, you have to do work against the force of gravity. • It is transformed into gravitational potential energy.

19. Newton’s Cradle • https://www.youtube.com/watch?v=d0HZ9N9yvcU

20. TCAP Practice Question 1 • When a lamp is turned on, only about 10% of the energy is transformed into light. What happens to the rest of the energy? • A The remaining energy is destroyed. • B Energy that is not transformed into light becomes thermal energy. • C The rest of the energy is changed into a solid state of matter. • D Energy is recycled back into the electrical circuit.

21. Answer • B

22. TCAP Practice Question 2 • Which best demonstrates a transformation of chemical energy into mechanical energy? • A a marble rolling down a track • B a lantern burning fuel • C a match lighting a candle • D a motorcycle using gasoline

23. Answer • D

24. TCAP Practice Question 3 • Lighting a match is best described as a transformation of • A mechanical energy into potential energy. • B kinetic energy into potential energy. • C chemical energy into light and heat energy. • D electrical energy into heat and chemical energy.

25. Answer • C

26. TCAP Practice Question 4 • A solar panel absorbs energy from the sun and transforms some of the energy into electrical energy. Which best explains what happens to the remaining energy? • A The remaining energy increases. • B The remaining energy is destroyed. • C The remaining energy is absorbed into the air. • D The remaining energy changes into other forms.

27. Answer • D

28. TCAP Practice Question 5 • Which best explains the energy transformation that occurs when sunlight strikes a car? • A Solar energy is changed into electrical energy. • B Solar energy is changed into thermal energy. • C Solar energy becomes chemical energy. • D Solar energy becomes mechanical energy.

29. Answer • B