Simple Simple MachinesMachines

WORKMechanical Advantage

Force

Effort Efficienc

y

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GoalsGoalsAnalyze the simple machines Analyze the simple machines

qualitqualitatively and atively and quantquantitatively in itatively in terms of force, distance, work and terms of force, distance, work and

mechanical advantagemechanical advantageBe able to calculate mechanical Be able to calculate mechanical

advantageadvantage

Be able to calculate amount of Be able to calculate amount of work done by a simple machinework done by a simple machine

Explain the different types of Explain the different types of simple machines.simple machines.

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WorkWorkTransfer of Energy from one Transfer of Energy from one

place to another.place to another.Applying a force over a Applying a force over a

certain distance.certain distance.Calculating Work:Calculating Work:

Work= Force x distanceWork= Force x distanceW = f x dW = f x d

FLASH FLASH

BACKBACK

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6 types of simple machines

Simple Machines Lever

Inclined Plane

Screw

Wedge

Wheel and Axle Pulley

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clip

What is a machineWhat is a machine??

A device that makes A device that makes work easierwork easier..

What is a simple machineWhat is a simple machine??

--a machine that does work a machine that does work with only one movementwith only one movement..

You still do the same amt of You still do the same amt of work —it’s just easierwork —it’s just easier!!

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1.1.Multiply the force you Multiply the force you apply.apply.A Car JackA Car Jack

2.2.Change the direction of Change the direction of the force.the force.BlindsBlinds

A machine can make A machine can make work easier in two work easier in two

ways:ways:

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Mechanical Mechanical AdvantageAdvantageNumber of times the Number of times the

machine multiplies the machine multiplies the effort forceeffort force (The (The

force you apply to it)force you apply to it)

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CLIP

Machines are a “give and take relationship.” If

you get your force multiplied, then you must go a greater

distance.

Watch for this in all Simple machines:8

Efficiency of a Efficiency of a MachineMachine

NEVER OVER 100%

90 J .100 J

A measure (%) of how much

work put into a

machine is actuallyactually

changed to useful work put out by

the machine.

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Ideal machineIdeal machine

Does not exist.Does not exist.

Efficiency =100%Efficiency =100%MA= 100%MA= 100%

FRICTIONFRICTION

According To “The Law According To “The Law of Conservation of of Conservation of

Energy” Can this exist?Energy” Can this exist?

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Types of MachinesTypes of MachinesLeversA lever is a

bar that is free to pivot, or turn about a fixed point.

How can we use levers?

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Levers

Resistance ArmEffort Arm

Resistance Force

Resistance Distance

FulcruFulcrumm

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Effort Force

Effort Distance

LOAD

LeversLeversThere are three types of LeversBased on the position of the

fulcrum

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LeverLeverss

The fulcrum is between the resistance force and the effort force.

1st Class:1st Class: Crowbars, pliers, scissors, seesaw

The closer the fulcrum The closer the fulcrum to the resistance to the resistance

force, the more the force, the more the lever multiplies the lever multiplies the

force.force.

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LeverLeverss

2nd Class: The resistance force is between the effort force and the fulcrum.

•Wheelbarrow•Nutcrackers•Crowbar (forcing two objects apart) •The handle of a pair of nail clippers

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3rd Class: the effort force is between the resistance force and the fulcrum.

LeverLeverss

•Hoe •Your arm •Catapult• Fishing rod•Tongs (double lever) (where hinged at one end)

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Mechanical Advantage of Mechanical Advantage of LeversLevers

As the length of the effort arm increases, the MA of the lever increases.

Effort arm

Resistance arm

5/5=1

10/5=2

20/5=4

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REVIEW

Position of Fulcrum

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PulleyPulleyss

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• What is a pulley?• A pulley is a grooved wheel with a rope or

chain running along the groove.• What can a pulley be used for?

Pulleys

1.Multiply the effort force

2.2.change the change the direction of the direction of the forceforce

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Pulleys Two types of Pulleys:

1. Fixed pulley– A pulley that is attached to something– Only changes the direction of the

force

2. Movable pulley– The pulley is free to move

***Block and Tackle***Combination of both types of pulleys

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Mechanical Advantage Mechanical Advantage of Pulleysof Pulleys

Effort Force

resistance Force

MA

=1

10 N

10 N

Only changes the direction of the force

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Mechanical Advantage of Mechanical Advantage of PulleysPulleys

MA

=2

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Mechanical Advantage of Mechanical Advantage of PulleysPulleys

MA

=2

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Mechanical Advantage of Mechanical Advantage of PulleysPulleys

MA =425

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Inclined Inclined PlanePlane

A sloping surface that that reduces the amount of force required to raise and object.

Effort Distance (l)Effort Distance (l)

Resis

tan

ce

Resis

tan

ce

Dis

tan

ce (h

)D

ista

nce (h

)

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Mechanical Advantage of Mechanical Advantage of Inclined PlanesInclined Planes29

Effort Distance (l)Effort Distance (l)

Resis

tan

ce

Resis

tan

ce

Dis

tan

ce (h

)D

ista

nce (h

)

Mechanical Advantage of Mechanical Advantage of Inclined PlanesInclined Planes30

Wheel and Axle• Consisting of two wheels of different sizes

that rotate together• The effort force is applied to the larger

wheel

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Ideal Mechanical Advantage = Radius of wheel    Of wheel and axel         Radius of axel

Gears are wheels with teeth.

Screw•An inclined plane wrapped

around a cylinder•The inclined plane lets the

screw slide into the wood.

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Examples: Bolt, Spiral Staircase

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Wedge• An inclined plane with one or

two sloping sides.• Changes the direction of the

effort force.

Effort Force

Resistance force

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Examples: Axe, Zipper, Knife

35 Review

Clip

36 Rube Goldburg

CLIP

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A 25B 10C 5D 4

A lever is used to lift a box. The mechanical advantage of the lever is

50 cm

10 cmOR

It took only 200 N It took only 200 N of force to lift a of force to lift a 1000N object, 1000N object, therefore the therefore the machine machine multiplied the multiplied the force 5 times!force 5 times!

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What is the amount of useful work output of a 25% efficient bicycle if the amount of work

input is 88 N-m?A 2200 N-mB 113 N-mC 63 N-mD 22 N-m

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.25 =Wout

88 J

Which of the following is an example ofa compound machine?

A bicycleB crowbarC doorknob

D ramp

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