Work & Power NOTES. Define / Describe WORK Work is the transfer of Energy that occurs when a force...
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Transcript of Work & Power NOTES. Define / Describe WORK Work is the transfer of Energy that occurs when a force...
![Page 1: Work & Power NOTES. Define / Describe WORK Work is the transfer of Energy that occurs when a force makes an object move. Work happens when a force moves.](https://reader035.fdocuments.us/reader035/viewer/2022062317/5a4d1b277f8b9ab05999774e/html5/thumbnails/1.jpg)
Work & Power
NOTES
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Define / Describe WORK
•Work is the transfer of Energy that occurs when a force makes an object move.
•Work happens when a force moves an object over a distance.
•If the object does not move, NO work is done!
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IMPORTANT• Work is the transfer of energy.
– If work is done on an object its energy will INCREASE
– If work is done by an object its energy will DECREASE
• If you are given an amount of work, you also know the amount of energy that has moved
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Two things must happen for work to be done.
What are they?•A force must be applied to
an object•The object must move in the
same direction as the force.
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Wrap –UP #1:Is work being done?
1. Lifting a spoonful of soup to your mouth.
2. Holding a stack of books motionless over your head
3. Letting a pencil fall to the ground.4. A person shovels snow off a
sidewalk.5. A person carries a bundle of
bricks across a construction site.
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1. Lifting a spoonful of soup to your mouth.Yes
2. Holding a stack of books motionless over your head
NO- no distance3. Letting a pencil fall to the ground.
YES- by gravity4. A person shovels snow off a sidewalk.
YES5. A person carries a bundle of bricks across a
construction site. NO- arms don’t move
Wrap –UP #1:Is work being done?
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Work Formula & SI UnitsWork = Force x Distance
W = F x dForce: Newton (N)Distance: meter (m)Work: Joule (J)
1 J = 1 N ·m
W
F d
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1. W=20J force=? d=2m
2. work=? F= 10N d= 500m
3. W=5000J F= 500N distance=?
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1. W=20J force=? d=2m F = W/d = 20J/2m = 10 N
2. work=? F= 10N d= 500m
3. W=5000J F= 500N distance=?
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1. W=20J force=? d=2m F = W/d = 20J/2m = 10 N
2. work=? F= 10N d= 500m W = F x d = 10 N x 500 m = 5000 J
3. W=5000J F= 500N distance=?
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1. W=20J force=? d=2m F = W/d = 20J/2m = 10 N
2. work=? F= 10N d= 500m W = F x d = 10 N x 500 m = 5000 J
3. W=5000J F= 500N distance=? d = W/F
= 5000J/ 500N= 10 m
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Wrap-Up #2: Sample Calculation
• A father lifts his daughter 2.0 m and exerts a force of 190 N. How much work does he do?
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• A father lifts his daughter 2.0 m and exerts a force of 190 N. How much work does he do?
• F = 190 N• D = 2.0 m W = F x d
= 190 N x 2.0 m W = 380 J
Wrap-Up #2: Sample Calculation
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Power•Power is the rate of doing work.– How much work is done in a
certain amount of time
Power = Work time
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P = Wt
Work: Joule (J)Time : seconds (s)Power: Watt (W)
1 Watt = 1 J/s
W
P t
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1. P = 200 W W=2000 J t=?
2. P =15 W Work= ? t= 10 sec
3. P= ? W= 56 J t= 2 sec
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1. P = 200 W W=2000 J t=? t = W/P = 2000J/200W = 10 sec
2. P =15 W Work= ? t= 10 sec
3. P= ? W= 56 J t= 2 sec
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1. P = 200 W W=2000 J t=? t = W/P = 2000J/200W = 10 sec
2. P =15 W Work= ? t= 10 sec W = P x t = 15 W x 10 sec
= 150 J3. P= ? W= 56 J t= 2 sec
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1. P = 200 W W=2000 J t=? t = W/P = 2000J/200W = 10 sec
2. P =15 W Work= ? t= 10 sec W = P x t = 15 W x 10 sec
= 150 J3. P= ? W= 56 J t= 2 sec
P = W/t = 56 J/ 2 sec = 28 W
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Wrap-Up #3: Power Calculation
• It takes 3, 150 Joules of work to move a refrigerator. If this is done in 5 minutes, how much power was used to move the refrigerator?
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• It takes 3, 150 Joules of work to move a refrigerator. If this is done in 5 minutes, how much power was used to move the refrigerator?
• W= 3, 150 J• t= 5 min x 60s = 300 s• P = W/ t
= 3150 J/ 300 s = 10.5 Watts
Wrap-Up #3: Power Calculation
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• Suppose two students are asked to unpack identical cartons of books. One student completes the job in ten minutes, while the other takes twenty minutes.
– Which student did more work?
– Which student used more power?
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• Suppose two students are asked to unpack identical cartons of books. One student completes the job in ten minutes, while the other takes twenty minutes.
– Which student did more work?•Both students did the same amount of work
– Which student used more power?
![Page 24: Work & Power NOTES. Define / Describe WORK Work is the transfer of Energy that occurs when a force makes an object move. Work happens when a force moves.](https://reader035.fdocuments.us/reader035/viewer/2022062317/5a4d1b277f8b9ab05999774e/html5/thumbnails/24.jpg)
• Suppose two students are asked to unpack identical cartons of books. One student completes the job in ten minutes, while the other takes twenty minutes.
– Which student did more work?•Both students did the same amount of work
– Which student used more power?•The one who finished in ten minutes