Work And Power
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Work and Power In physics, work is defined two ways: 1. Work is done on an object when a force acting parallel (or some component of the force acting parallel) causes an object to move. The distance the object moves must be parallel to the force or some component of the force.
W = Fll ∆ d
units: N•m or joule (J)
We describe the work being done on one object by another.
2. Work is also defined as a transfer or transformation of energy. When energy is transferred from one object to another, work is done.
W=∆ E
units: N•m or joule (J)
…..But what is energy? More on that later!
• Work done… a weightlifter lifts a barbell Force and distance are parallel! Fg * ∆ h = Work
• No work done… a weightlifter stands with a barbell overhead Force and distance are not parallel! There is a force but the barbells do not move.
Power is the rate at which work is done. P= W/∆ t units: J/sec, watt (W)
So what is horsepower?
1 Hp =746 watts
“The term horsepower was invented by the engineer James Watt. Watt lived from 1736 to 1819 and is most famous for his work on improving the performance of steam engines. The story goes that Watt was working with ponies lifting coal at a coal mine, and he wanted a way to talk about the power available from one of these animals. He found that, on average, a mine pony could do 22,000 foot-pounds of work in a minute. He then increased that number by 50 percent and pegged the measurement of horsepower at 33,000 foot-pounds of work in one minute. It is that arbitrary unit of measure that has made its way down through the centuries.”
http://www.howstuffworks.com/horsepower1.htm
Work Sample Problem I apply a 40.0 N force 35° below the horizontal to the 13 kg overhead projector cart. The cart moves a distance of 5.0 meters at a constant velocity. The wheels are locked and the cart slides across the floor, µ = 0.217. • How much work do I do on the cart? • How much work does friction do on the cart? • If the cart is moved in a time of 24 seconds, how much power do I generate?
Horsepower Lab • Today in lab, you will determine your horsepower during various activities. – The Stairmaster – Weightlifter – Chairmaster – Drop and give me 20!
• How will you calculate the work done during each activity?
W = Fll∆ d What force has to be exerted in each of these activities to move the object?
W = Fll ∆ d
units: N•m or joule (J)
We describe the work being done on one object by another.
2. Work is also defined as a transfer or transformation of energy. When energy is transferred from one object to another, work is done.
W=∆ E
units: N•m or joule (J)
…..But what is energy? More on that later!
• Work done… a weightlifter lifts a barbell Force and distance are parallel! Fg * ∆ h = Work
• No work done… a weightlifter stands with a barbell overhead Force and distance are not parallel! There is a force but the barbells do not move.
Power is the rate at which work is done. P= W/∆ t units: J/sec, watt (W)
So what is horsepower?
1 Hp =746 watts
“The term horsepower was invented by the engineer James Watt. Watt lived from 1736 to 1819 and is most famous for his work on improving the performance of steam engines. The story goes that Watt was working with ponies lifting coal at a coal mine, and he wanted a way to talk about the power available from one of these animals. He found that, on average, a mine pony could do 22,000 foot-pounds of work in a minute. He then increased that number by 50 percent and pegged the measurement of horsepower at 33,000 foot-pounds of work in one minute. It is that arbitrary unit of measure that has made its way down through the centuries.”
http://www.howstuffworks.com/horsepower1.htm
Work Sample Problem I apply a 40.0 N force 35° below the horizontal to the 13 kg overhead projector cart. The cart moves a distance of 5.0 meters at a constant velocity. The wheels are locked and the cart slides across the floor, µ = 0.217. • How much work do I do on the cart? • How much work does friction do on the cart? • If the cart is moved in a time of 24 seconds, how much power do I generate?
Horsepower Lab • Today in lab, you will determine your horsepower during various activities. – The Stairmaster – Weightlifter – Chairmaster – Drop and give me 20!
• How will you calculate the work done during each activity?
W = Fll∆ d What force has to be exerted in each of these activities to move the object?
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