1. Write Definitions for:
Work & Power
Write Definitions for:
Work
Power

2. In Terms of Physics, What is Happening Here?

3. Work
Work is done when there is movement against an opposing force.

4. *REMINDER* - How to do calculations
e.g. John took 5 s to run 200 m. Calculate his speed.
time = 5 s
distance = 200 m
Write down the information given
Decide which formula to use and write it down
Put the values into the formula
Calculate your answer
Add units!!!
speed = distance / time
speed = 200 / 5
speed = 40
speed = 40 m/s

5. Calculating Work Done Work done = force x distance moved (J) (N) (m)
What is work done on an object if a force of 300 N moves it 8 m?
How much work is done if an object weighing 900 N is moved up m by a crane?

6. Question 1
What is work done on an object if a force of 300 N moves it 8 m? Work done = force x distance moved Work = 300 x 8 Work = 2400 J

7. Question 2
How much work is done if an object weighing 900 N is moved up 100 m by a crane? Work done = force x distance moved Work done = 900 x 100 Work = J Work = 90 kJ

8. Which car has the most power?

9. Which car has the most power?
WRONG!!!!
This is not the Physics definition of power.

10. Which car has the most power?
Same weight.
Same hill.
Same amount of work.

11. Power
Power = work done
time taken
Power = watt (W)

12. Questions
A cat who weighs 40 N climbs a tree that is 15 m tall in 10 s. Calculate the work done by the cat and the cat’s power.
Oliver weighs 600 N. He climbs a flight of stairs that is 3.0 m tall in 4.0 seconds. What was Oliver’s power in watts?

13. Work done = Force x Distance
Questions
A cat who weighs 40 N climbs a tree that is 15 m tall in 10 s. Calculate the work done by the cat and the cat’s power.
Work done = Force x Distance
Work done = 40 x 15 = 600 J
Power = Work done/time
Power = 600 / 10 = 60 W

14. Questions
2. Oliver weighs 600 N. He climbs a flight of stairs that is 3.0 m tall in 4.0 seconds. What was Oliver’s power in watts? Work done = Force x Distance Work done = 600 x 3.0 = J Power = Work done/time Power = / 4.0 = 450 W

15. Relay Race Work in pairs.
Collect a question from your envelope at the front of the room.
Answer the question.
Return the question and collect another one.
Rules
Only 1 Q from the envelope at a time.
Must return a Q before collecting another one.
No running.

16. Conservation of Energy & Efficiency

17. Puzzle
Which one of the nine types of energy does your body definitely not have right now?
Answer: light. Except actually, we do glow in the dark – very slightly. See for example:
As for the other types of energy: kinetic, thermal and sound are obvious. Gravitational potential because we are on the Earth’s surface (think of falling down a well), electrical in our nerves, chemical potential in our cells ready for conversion when needed, elastic potential in flexed muscles, and nuclear (potential) energy stored in the nuclei of our cells (though I wouldn’t expect all students to get that last one).

18. The Burning Question of the day:
When a candle is burning, the chemical potential energy stored in the wax is turning into heat and light energy.
Eventually the candle burns out.
What do you think has happened to the energy that was originally stored in the wax? Is it still around somewhere? Could we get it back? Or has it ceased to exist?

19. And:
A book is on a shelf. The book has gravitational potential energy.
If the book falls off the shelf, its gravitational potential energy turns into kinetic energy as it falls, so it speeds up.
Then it lands, and stops moving. Has its energy disappeared from existence? Or has it turned into something else, or gone somewhere else?
You could also discuss the idea of trying to keep some energy in a box. Which types can you keep indefinitely? If you yell into a box and close the lid, is the sound (energy) still there when you reopen the box later? (It would make a great practical joke if it could be unleashed on an unsuspecting friend…) What if you shone a torch into the box and sealed it, or heated up the box’s contents? The energy doesn’t stay around; in fact, it all ends up as heat, which spreads out into the room, the atmosphere, and eventually all of the universe. The only types of energy you can store are the different types of potential energy.

20. IR Images of Ball Before and After Bouncing

21. Background: James Joule
James Joule has the unit of energy named after him because of his experiments on energy transformations. He postulated that heat, movement, etc. were all forms of energy, and could be transformed into each other. The story (which may not be true) goes that on his honeymoon he visited a waterfall in Switzerland and measured its temperature at the top and bottom. He was expecting the temperature at the bottom to be greater (which it is, though it requires very sensitive equipment to measure this).

22. Background: Joule’s Experiment
An experiment to test the law of conservation of energy. The weights drop, causing their gravitational potential energy to be converted into kinetic energy. The wooden drum turns, which turns the paddle and raises the temperature of the water. The container of water was insulated to minimise the rate of heat loss.

25. Efficient
In both video/clips/adverts they were talking about energy saving and a key word efficient.
What does efficient mean? Discuss with your partner and write a definition in your book. (2mins)