2 W = F • d CLIP Unit= Joule

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

he shared in discovering the law of the conservation of energy. 4 In 1840, he 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

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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W = F • d = (400 N) • (0.25 m) Calculating Work 8 When doing a chin-up, a physics student lifts her 40-kg body a distance of 0.25 meters in 2 seconds. How much work is done by the student's biceps? W = F • d = (400 N) • (0.25 m) W = 100 J

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.

11 James Watt son of a merchant, born in Greenock, Scotland, in 1736 In 1757 he 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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13 suppose that a 40-horsepower engine could accelerate the car from 0 mi/hr to 60 mi/hr in 16 seconds. if this were the case, then a car with four times the horsepower could do the same amount of work in one-fourth the time. that is, a 160-horsepower engine could accelerate the same car from 0 mi/hr to 60 mi/hr in 4 seconds.

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

16 W = F • d = (400 N) • (0.25 m) W = 100 N-m W = 100 J When doing a chin-up, a physics student lifts her 40-kg body a distance of 0.25 meters in 2 seconds. What is the power delivered by the student's biceps? The work done to lift her body is W = F • d = (400 N) • (0.25 m) W = 100 N-m W = 100 J The power is the work/time ratio which is (100 J) / (2 seconds) = 50 Watts.

Torque 17 A measure of how much a force acting on an object causes that object to rotate. A torque is a force exerted at a distance from the axis of rotation; the easiest way to think of torque is to consider a door. When you open a door, where do you push? If you exert a force at the hinge, the door will not move; the easiest way to open a door is to exert a force on the side of the door opposite the hinge, and to push or pull with a force perpendicular to the door

Torque 18