2 CLIP TRANSFER OF ENERGY W = F • d Unit= Joule

James Prescott Joule (December 24, 1818–October 11, 1889) was an English physicist. 3 Educated at home sent to Cambridge at the age of 16 to study with the British chemist John Dalton 1850-established the equivalence between amounts of heat and mechanical work with his famous "paddle-wheel experiment". Also established the cooling effect that occurs when a gas is rapidly expanded, an effect that is used in refrigeration systems.

Shared in discovering the law of the conservation of energy. 4 1840- stated a law, now called Joule's Law, that heat is produced in an electrical conductor. The International unit of energy, the joule, is named in his honor. Among his many inventions are "arc" or electrical welding and the displacement pump.

5 For there to be work on an object, there must be a displacement and the force must cause that displacement

Atlas holds up the Earth But he doesn’t move, dist = 0 He doesn’t do any work!

The waiter does work when he picks up the tray but not while he carries it around the room dist is not zero, but dist. the tray travels is 0

Is work done here? pushing on a wall pushing a boat out to sea 6 Is work done here? pushing on a wall pushing a boat out to sea lifting up a box holding up a box

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Calculating Work 8

9 Work has nothing to do with the amount of time that this force acts to cause the displacement. Sometimes, the work is done very quickly and other times the work is done rather slowly.

POWER The rate of energy transfer. How fast work is done. 10 The rate of energy transfer. How fast work is done. Machines with different power ratings do the same amount of work...just in different amounts times.

A man who can lift 50 N of weight in 10 seconds or a woman who can lift 50 N of weight in 8 seconds?

11 James Watt Son of a merchant, born in Greenock, Scotland, in 1736 -1757:established his own mathematical instrument-making business Watt discovered how he could make the steam engine more efficient by cooling the used steam in a condenser that was separate from the main cylinder. This made them faster, safer, and more economical, resulting in steam overtaking water-power as the main source of energy. James Watt Unit of power is the Watt Watt calculated that a horse exerted a pull of 180 lb., therefore, when he made a machine, he described its power in relation to a horse, i.e. "a 20 horse-power engine".

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14 watt (W) 1W = 1 J/s One watt is equal to a power rate of one joule of work per second of time. 1Kilowatt = 1000 Watts

15 Calculating Power

A new conveyor system at the local packaging plant will utilize a motor-powered mechanical arm to exert an average force of 890 N to push large crates a distance of 12 meters in 22 seconds. Determine the power output required of such a motor. 16

Hockey: Work and Power