1. Work and Power Efficiency, Newton, Joules, Watts, Joules per second

2. Work Work is done whenever a force is used to move an object.

3. Work Work is done whenever a force is used to move an object. More work is done if bigger forces and larger distances are used

4. Work Work is done whenever a force is used to move an object. More work is done if bigger forces and larger distances are used Work done (J) = Force (N) X Distance (m)

5. Calculations The key to doing questions on work is to remember that it is a Force.

6. Example A forklift raises 4 bags of cement, each with a mass of 25kg, by 3 meters. What is the work done by the forklift?

7. Example A forklift raises 4 bags of cement, each with a mass of 25kg, by 3 meters. What is the work done by the forklift? Work = force x distance

8. Example A forklift raises 4 bags of cement, each with a mass of 25kg, by 3 meters. What is the work done by the forklift? Work = force x distance Force, this is weight NOT mass, that’s the trick

9. Weight not mass 4 bags 25kg a bag 4 x 25 = 100kg Weight = mass x gravity On Earth we take ‘g’ to be 10 Therefore weight = 100 x 10 = 1000N

10. Solution Work = Force x distance 3000N = 1000N x 3m

11. Try this Find how much work you would go to lift yourself onto the wooden box What do you need to measure? weight distance

12. Power Power is the work done every second

13. Power Power is the work done every second When dealing with power just think light bulbs…. 60W or 100W….which is more powerful? 100W = 100J of energy every second So Watts also = J/s

14. Power Try the experiments around the room Formula for Work done and Power Work done = force x distance Power = Work done time

15. Consider this question A builder lifts 100 bags of cement, each with a mass of 25kg, up flights of stairs with a total height of 5m. It takes him 1 and a quarter hours to do this. What is his average power?

16. Answer and method 100 bags @ 25kg = 2500kg

17. Answer and method 100 bags @ 25kg = 2500kg 2500kg x g = weight (weight = m x g) 2500 x 10 = 25000N (g = 10 on Earth)

18. Work done Work done = force x distance = 25000 x 5 = 125000J

19. Power First convert time to seconds! 1.25 hours, into seconds? 1 min = 60 sec 1 hour = 60 min 1 hour = 60 x 60 =3600 1.25 hours = 60x60x1.25=4500 seconds

20. Power Power = work done / time Power = 125000 4500 Builder power = 27.778 W (less than a 30W bulb!!)

21. Experiments around the room Calculate your power in each of the exercises situated around the room. You need at least 2 people at each station, one to do time reading and one to do the exercise.

22. Power up the stairs Run up the stairs, time how long it takes

23. Power up the stairs Run up the stairs, time how long it takes Find your weight (mass x g)

24. Power up the stairs Run up the stairs, time how long it takes Find your weight (mass x g) Find the height of the stairs