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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. Work and Power Introduction Work and Power Problems No Lab 4/3, 4/4, and 4/5 Lab on 4/7
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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. • 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 Agenda:
Work • Work • is defined as the product of the force exerted on an object and the distancethe 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.
WorkCHECK YOUR NEIGHBOR If you push against a stationary brick wall for several minutes, you do no work • on the wall. • at all. • both of the above • none of the above Explain your answer to your neighbor.
WorkCHECK YOUR ANSWER If you push against a stationary brick wall for several minutes, you do no work • 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
WorkCHECK YOUR NEIGHBOR Work is done in lifting a barbell. How much work is done in lifting a twice-as-heavy barbell the same distance? • Twice as much • Half as much • The same • It depends on the speed of the lift. Explain your answer to your neighbor.
WorkCHECK YOUR ANSWER Work is done in lifting a barbell. How much work is done in lifting a twice-as-heavy barbell the same distance? • 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.
WorkCHECK 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 • less than twice as much. • twice as much. • more than twice as much. • zero. Explain your answer to your neighbor.
WorkCHECK 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 • less than twice as much. • 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)
PowerCHECK YOUR NEIGHBOR A job can be done slowly or quickly. Both may require the same amount of work but different amounts of • energy. • momentum. • power. • impulse. Explain your answer to your neighbor.
PowerCHECK YOUR ANSWER A job can be done slowly or quickly. Both may require the same amount of work but different amounts of • energy. • momentum. • power. • impulse. Comment: Power is the rate at which work is done.
