Download - Physical Science: Work
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Work
Chapter 5.1
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What is work?• You work on math problems.• You go to work.• Making a sandwich is work.• Taking out the trash is too much
work.• Doing your homework is work.
• What machines help us work?
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In physics, work is:• *Work is a formula: W=Fd
• *W= Work; F= Force; d= distance
• *Example:
• *Moving an object with a force of one newton for a distance of one meter= one joule of work
• *A joule is a unit that measures work
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Distance (m)
W = F x d
Force (N)
Work (joules)
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Brainstorm using a circle map:
1. In the Center write: Work
2. In the circle write types of simple machines
3. In the frame of reference write down what work these machines do
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Input and Output• *Input = how much force you put
into doing work
• *Output = how much work was done
• *The work output can never exceed the work input!
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Work:
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Efficiency• *Efficiency is the fraction of
incoming energy that goes into a process.
Examples: Fuel mileage, appliances and energy efficiency
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*Efficiency
• What does it mean to be efficient?
• *In a very efficient machine, all or most of the work input becomes work output
• In other words…if five joules of work was used to lift a box, the box would move the equivalent of five joules output- nothing was wasted.
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What about friction?
• *In the real world- Work Output is always less than work input.– WHY?
• *Forces like friction use up some of the input work– Example: wheel turning on an axle can
get very hot…when the wheel gets hot some of that input work is being converted to heat.
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Friction
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*What is Power?• *Power is the rate at which work
is done.P = W t Time (sec)
Work (joules)
Power (watts)
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Power:
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Power Demo
• These two people did the same amount of work.
•The difference is Power: One person used more Power and got the work done much faster
•A more powerful machine does the same amount of work in less time
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Review:• Work = Force x distance
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Your Turn…
• On your paper:–Look through Chapter 5, Section 1
Pg 85-90
–Add more information from this section into your notes.
(at least six items)
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Practice:
• Skill Sheet 5-AExample:
• How much work is done on a 10 N block that is lifted 5 meters off the ground by a pulley?
Work = F x d
W = 10N x 5 meters = 50 newton- meters OR 50 joules
Remember: newton-meters = joules
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Work
• Work = Force x Distance
• Work is only done when something is moved a distance in the direction of the force.