ENERGY

1. ENERGY Energy is the ability to do work.

2. ENERGY • The units of energy are: • Joule • calorie (4.2 Joule) • Kilocalorie • Also known as a food calorie • Often written as Calorie in the United States

3. FOOD LABELS IN UK

4. DOG FOOD LABEL US BENEFUL DOG FOOD

5. ACTIVITY JOULE OF A COOKIE

6. Question How many Joules of energy are stored in a candy bar which contains 250 food calories? A. 250000 B. 1050 kJ C. 840 kJ D. 420000 J

7. ENERGY The forms of energy are: Heat Light Electrical Chemical • Sound • Nuclear • Mechanical

8. ENERGY Energy can be converted into work or from one form to another.

9. ENERGY Conservation of Energy In any process, energy can not be created or destroyed. It can only be converted from one form to another.

10. ENERGY • MECHANICAL ENERGY • The sum of the potential energy and kinetic energy of an object • POTENTIAL ENERGY • Energy of position • KINETIC ENERGY • Energy of motion

11. ENERGY POTENTIAL ENERGY normally associated with the work required to lift an object or distort an elastic object

12. ENERGY GRAVITATIONAL POTENTIAL ENERGY (GPE) • Is equal to the work required to lift an object GPE = Weight X Height

13. Video GPE OF SAND MOVING A TOY

14. ENERGY • Question • A 500 N girl stands on a diving platform 10 meters above the water. A 1000 N boy stands on the platform 5 meters above the water. Which possesses the most GPE? • Answer – neither, the GPE is the same for both

15. ENERGY ELASTIC POTENTIAL ENERGY (EPE) • Is equal to the work required to bend or stretch an object

16. Video EPE IN A POLE VAULT

17. ENERGY KINETIC ENERGY (KE) • The kinetic energy of an object depends on its mass and velocity (speed). KE = ½ (mass) (velocity)2

18. ENERGY HOW TO FIND THE INCREASE IN KINETIC ENERGY OF AN OBJECT WHEN ITS SPEED CHANGES KE1/KE2 = ½ m V12 / ½ m V22 KE1/KE2 = V12 / V22 KE1/KE2 = (V1/ V2)2

19. ENERGY TO FIND BY WHAT FACTOR THE KE CHANGES, FIND THE FACTOR FOR THE SPEED AND SQUARE IT

20. ENERGY Question • How much more kinetic energy does a car have at 60 mph as compared to 30 mph? • Answer: four times as much kinetic energy

21. ENERGY • Conservation of energy in mechanical systems • The energy you start with equals the energy you finished with plus any work done. • KEf + PEf = KEs + PEs + Work

22. ENERGY • Conservation of energy in a pendulum • PhET Simulation “Pendulum Lab”

23. ACTIVITY KINETIC PENDULUM POTENTIAL POPPER

24. ENERGY • Conservation of energy in a mass on a spring • PhET Simulation “Mass – Spring Lab”

25. ENERGY • Conservation of energy on a track or roller coaster • PhET Simulation “Energy – Skate Park””

26. ACTIVITY MECHANICAL ENERGY USING PhET

27. VIDEO ROLLER COASTER

28. 5 1 3 4 2 QUESTION A pendulum is pulled to point 1. It is released from rest and allowed to swing back and forth. If the pendulum possesses 100 joules of energy, which point listed below is assigned the wrong value for the PE or KE? 5 1 4 3 2 • Point 5 - KE = 100 J • Point 4 - PE = 50 J • Point 3 - KE = 100 J • Point 2 - KE = 50 J • Point 1 - PE = 100 J

29. POWER Power is the rate of doing work.

30. Video Human Power

31. POWER • Power can be found by dividing the amount of work (W) done by the amount of time (t) required to do the work. P = W / t

32. ACTIVITY

33. POWER • The unit of power is the watt in ISU. • Watt = Joule / second • The unit of power in the British system is the horsepower. • Horsepower = 750 Watt • 550 foot pound per second

34. POWER • Questions • Which can do more work, a 100 kw motor or a 200 kW motor? • If a 100 kW motor can lift an elevator from the first to the fourth floor in 10 seconds, how long will it take a 200 kw motor to lift the same elevator the same distance?

35. SUMMARY • FORCE • WORK • ENERGY • FORMS • CONSERVATION OF ENERGY • MECHANICAL SYSTEMS • POWER