Do now!

1. He’s going to blow! Be careful Neutral Good Excellent MOODOMETER Can you read through the work you did last lesson? Do now!

2. Today’s lesson • Calculating Gravitational Potential energy • Calculating kinetic energy

3. But first!

4. A reminder • Energy cannot be made or destroyed, only transformed (changed). • Energy is measured in Joules. That’s me!

5. Types of Energy Heat Chemical Light Gravitational Sound Elastic/strain Kinetic Nuclear Electric Stored/potential

6. Lifting objects When we lift objects, we are doing work because a force is moving. Force Distance moved

7. Work done = Force x Distance Another sexy physics formula to learn!

8. Work done (J) = Force (N) x distance (m) A man lifts a mass of 120 kg to a height of 2.5m. How much work did he do? Force = weight = 1200N Work = F x d = 1200 x 2.5 Work = 3000 J

9. Work done (J) = Force (N) x distance (m) A man lifts a mass of 120 kg to a height of 2.5m. How much work did he do? Work = mass x g x height

10. Chemical kinetic gravitational Gain in GPE = work done = m x g x h Work = mass x g x height

11. Gravitational potential energy Ep = mgh m kg J N/kg or m/s2 Can you copy this please?

12. Example Woof! (help!) A dog of mass 12 kg falls from an aeroplane at a height of 3.4 km. How much gravitational energy does the dog have as it leaves the aeroplane?

13. Example On earth g = 10 m/s2 Mass of dog = 12 kg Height = 3.4 km = 3400 m

14. Example On earth g = 10 m/s2 Mass of dog = 12 kg GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J Height = 3.4 km = 3400 m

15. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J Just before the dog hits the ground, what has this GPE turned into?

16. Kinetic energy

17. Kinetic energy Kinetic energy of an object can be found using the following formula Ek = mv2 2 where m = mass (in kg) and v = speed (in m/s)

18. Example A bullet of mass 150 g is travelling at 400 m/s. How much kinetic energy does it have?

19. Example A bullet of mass 150 g is travelling at 400 m/s. How much kinetic energy does it have? Ek = mv2/2 = (0.15 x (400)2)/2 = 12 000 J

20. Energy changes

21. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

22. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J KE at bottom = 408 000 J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

23. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J KE at bottom = 408 000 J = mv2/2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

24. Example 408 000 = mv2/2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

25. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

26. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 816000 = 12v2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

27. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 816000 = 12v2 68000 = v2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

28. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 816000 = 12v2 68000 = v2 261 = v v = 261 m/s Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

29. Let’s try some questions! Page 83 questions 1, 2, 3 and 4.