Do Now Have you ever performed work before
Do Now: • Have you ever performed work before? • Describe the situation. • How did you know that you performed work?
Objective: • Be able to distinguish and describe work and power. Agenda: • • Work and Power Introduction Work and Power Problems No Lab 4/3, 4/4, and 4/5 Lab on 4/7 Six Flags Permission Slips by Wednesday
Work • Work – is defined as the product of the force exerted on an object and the distance the object moves (in the same direction as the force). – is done only when a force succeeds in moving the body it acts upon.
Work • Two things enter where work is done: – Application of force – Movement of something by that force • The work done on the object is the average force multiplied by the distance through which the object is moved.
Work CHECK YOUR NEIGHBOR If you push against a stationary brick wall for several minutes, you do no work A. B. C. D. on the wall. at all. both of the above none of the above Explain your answer to your neighbor.
Work CHECK YOUR ANSWER If you push against a stationary brick wall for several minutes, you do no work A. B. C. D. on the wall. at all. both of the above none of the above Explanation: You may do work on your muscles, but not on the wall.
Work • The quantity of work done is equal to the amount of force times the distance moved in the direction in which the force acts. • Work falls into two categories: – Work done against another force – Work done to change the speed of an object
Work CHECK YOUR NEIGHBOR Work is done in lifting a barbell. How much work is done in lifting a twice-as-heavy barbell the same distance? A. B. C. D. Twice as much Half as much The same It depends on the speed of the lift. Explain your answer to your neighbor.
Work CHECK YOUR ANSWER Work is done in lifting a barbell. How much work is done in lifting a twice-as-heavy barbell the same distance? A. B. C. D. Twice as much Half as much The same It depends on the speed of the lift. Explanation: This is in accord with work = force × distance. Twice the force for the same distance means twice the work done on the barbell.
Work CHECK YOUR NEIGHBOR You do work when you push a cart with a constant force. If you push the cart twice as far, then the work you do is A. B. C. D. less than twice as much. more than twice as much. zero. Explain your answer to your neighbor.
Work CHECK YOUR ANSWER You do work when you push a cart with a constant force. If you push the cart twice as far, then the work you do is A. B. C. D. less than twice as much. more than twice as much. zero.
Energy • Energy is defined as that which produces changes in matter. • The effects of energy are observed only when it is being transferred from one place to another or transformed from one form into another. • Unit for energy: joule • Both work and energy are measured in joules.
Power • Power is a measure of how quickly work is done or the rate at which energy is changed from one form into another. • Equation for power: Units for power: joule per second, or watt (One watt = 1 joule of work per second)
Power CHECK YOUR NEIGHBOR A job can be done slowly or quickly. Both may require the same amount of work but different amounts of A. B. C. D. energy. momentum. power. impulse. Explain your answer to your neighbor.
Power CHECK YOUR ANSWER A job can be done slowly or quickly. Both may require the same amount of work but different amounts of A. B. C. D. energy. momentum. power. impulse. Comment: Power is the rate at which work is done.
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