Work,%20Power%20and%20Simple%20Machines

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Work
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Work has a special meaning in physics.
Work
Unlike your everyday experience, where you go to
an after school job and earn money, work in
physics does not pay for your car insurance.
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Work is done on an object
when a force is applied to an object and the
object is displaced.
Work is only done if the object moves a distance.
Do not confuse applying a force with doing work.
Pushing or pulling on an object may make you
sweat but you do no work unless it moves.
Work Force x displacement (cosine of angle for
the portion of the force parallel to the distance
traveled)
Only the force parallel to the direction of the
displacement does work.
Units Newton x Meter (Nm)
Work is a scalar quantity
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Read the following five statements and determine
whether or not they represent examples of work.
A teacher applies a force to a wall and becomes
exhausted.
NO
A book falls off a table and free falls to the
ground.
YES
A waiter carries a tray full of meals above his
head by one arm across the room. (Careful! This
is a tricky question.)
NO
A rocket accelerates through space.
YES
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Power
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In Physics Power is the Rate of Doing Work
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A watt is a small unit
If you lift a glass of water (2N) to your mouth
(0.5 m) in 1 second you do one joule of work and
you are doing work at rate of one watt
Since a watt is relatively small, power is often
measured in kilowatts (kW)
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Simple Machines
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Simple Machines
A simple machine is an object with few moving
parts that redirects an applied force to perform
work.
Usually a simple machine is used to reduce the
force needed to perform a task.
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Simple Machines and Rube Goldberg
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Work and Machines

• Force of Effort - Fe - The amount of force that
  is applied to the machine.
• Force of Resistance - Fr - The amount of force
  that the machine applies.
• Distance of Effort - de - The distance the force
  of effort is applied.
• Distance of Resistance - dr - The distance the
  machine applies the force.

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Force of Effort
Screw
Force of Resistance
Force of Resistance
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Incline Plane
Force of Effort
Force of Resistance
Distance of Effort
Distance of Resistance
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L e v e r
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Lever
F1 Fr Force of Resistance F2 Fe Force of
Effort
Fulcrum Pivot Point
D1 dr Distance of Resistance D2 de
Distance of Effort
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Lever Classes
First Class Lever
Effort - Fulcrum - Resistance
Second Class Lever
Fulcrum - Resistance - Effort
Third Class Lever
Fulcrum - Effort - Resistance
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First Class Lever
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PULLEY
Pulleys redirect the force of effort.
The number of pulleys and their arrangement can
reduce the amount of effort force needed to raise
a particular load.
The number of lifting strands will determine the
advantage to using a pulley system
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Pulleys
1 Lifting Strand
How many lifting strands for each pulley system?
2 Lifting Strands
2 Lifting Strands
3 Lifting Strands
3 Lifting Strands
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WEDGE
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Wheel and Axle
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Efficiency of Machines
Wi Work Input The Amount of Work applied to
the machine
FeForce of Effort
Wi Fede
deDistance of Effort
Wo Work Output the Amount of Work transferred
by the machine
FrForce of Resistance
Wo Frdr
drDistance of Resistance
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