Work, Power and Simple Machines

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Work, Power and Simple Machines
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Work
Force 40 N
Distance 10 m

• Force acting through a distance

W F d 40 N 10 m 400 Joules
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Work

• Force must be in same direction as distance

Force
Distance
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Work

• Force must be in same direction as distance

There is no work being done on the farmer
Force
Distance
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Power
400 J/1 sec 400 watts 400 J/5 sec 80 watts

• How fast (or the rate) Work is done

P W/t
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How do machines make work easier?
Work In Work Out
Increase F MAgt1
Increase D MAlt1
Change direction of F MA1
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Even though machines make work easier,

• they cannot change the amount of work

Work Input
Work Output
Feffortdistance
Fresistancedistance
Work Input is always greater than Work Output due
to Friction
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Even though machines make work easier,
Work Input is always greater than Work Output due
to Friction

• Efficiency Work Output / Work Input 100

Work Input
Work Output
Feffortdistance
Fresistancedistance
10N5m 50J
20N2m 40J
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Even though machines make work easier,
Work Input is always greater than Work Output due
to Friction

• Efficiency (40 J / 50 J) 0.8

Work Input
Work Output
Feffortdistance
Fresistancedistance
10N5m 50J
20N2m 40J
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Even though machines make work easier,
Work Input is always greater than Work Output due
to Friction

• Efficiency (40 J / 50 J) 0.8 100
• 80

Work Input
Work Output
Feffortdistance
Fresistancedistance
10N5m 50J
20N2m 40J
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Inclined Plane

• A slanted surface used to raise an object

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Inclined Plane
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Inclined Plane
5 N
5 N
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Inclined Plane
4 N
5 N
5 N
5 N

• Decreases the size of the effort force

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Inclined Plane
4 N
5 N
5 N
5 N

• Decreases the size of the effort force

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Inclined Plane
5 N
5 N
4 N
5 N

• Decreases the size of the effort force
• Increases the distance

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Wedge

• An inclined plane that moves

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Wedge

• An inclined plane that moves

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Wedge

• An inclined plane that moves

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Wedge

• An inclined plane that moves

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Wedge

• An inclined plane that moves

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Wedge

• An inclined plane that moves

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Wedge

• As a wedge moves through an object to be cut,

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Wedge

• A small effort force

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Wedge

• A small effort force
• Is able to overcome

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Wedge

• A small effort force
• Is able to overcome
• A large resistance force

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Wedge

• A small effort force
• Is able to overcome
• A large resistance force

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Wedge

• How can the mechanical advantage be increased?

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Wedge

• How can the mechanical advantage be increased?

Reduce the effort force by decreasing the angle
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Screw

• An inclined plane wrapped around a central bar or
  cylinder to form a spiral

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• How fast (or the rate) Work is done

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1st class
2 N
2 N

• Mechanical Advantage
• resistance F / effort F

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1st class
2 N
2 N

• Mechanical Advantage
• resistance F / effort F 2/2 1

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2nd class
1 N
2 N

• Mechanical Advantage
• resistance F / effort F

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2nd class
1 N
2 N

• Mechanical Advantage
• resistance F / effort F 2/1 2

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3rd class
3 N
2 N

• Mechanical Advantage
• resistance F / effort F

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3rd class
3 N
2 N

• Mechanical Advantage
• resistance F / effort F 2/3 0.66

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Pulleys
Fixed
5 N
5 N
Movable
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Pulleys
Fixed
MA 5/2.5 2
2.5 N
2.5 N
5 N
MA 5/51
5 N
5 N
Movable
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Pulleys
2.5 N
2.5 N
5 N
5 N
5 N
Resistance distance Effort distance
Resistance distance 1/2 Effort distance
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Wheel and Axle

• Two circular objects of different size
• The wheel always moves a greater distance than
  the axle

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Wheel and Axle

• Wheel Large Distance, Small Force
• Axle Small Distance, Large Force

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Compound Machine Corkscrew

• Inclined Plane?
• Wedge?
• Screw?
• Lever?
• Pulley?
• Wheel and Axle?

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Compound MachineCorkscrew

• Inclined Plane
• Wedge
• Screw
• Lever
• Pulley
• Wheel and Axle

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Compound Machine Drill

• Inclined Plane?
• Wedge?
• Screw?
• Lever?
• Pulley?
• Wheel and Axle?

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Compound Machine Drill

• Inclined Plane
• Wedge
• Screw
• Lever
• Pulley
• Wheel and Axle

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Compound MachineJack

• Inclined Plane?
• Wedge?
• Screw?
• Lever?
• Pulley?
• Wheel and Axle?

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Compound MachineJack

• Inclined Plane
• Wedge
• Screw
• Lever
• Pulley
• Wheel and Axle