P. Sci.P. Sci.Unit 3Unit 3

MachinesMachines

2

What’s work?What’s work? A scientist delivers a speech to an audience of his A scientist delivers a speech to an audience of his

peers. peers. NoNo A body builder lifts 350 pounds above his head. A body builder lifts 350 pounds above his head. YesYes A mother carries her baby from room to room. A mother carries her baby from room to room. NoNo A father pushes a baby in a carriage. A father pushes a baby in a carriage. YesYes A woman carries a 20 km grocery bag to her car? A woman carries a 20 km grocery bag to her car? NoNo

Machine – a device that Machine – a device that makes doing work easier makes doing work easier by…by…

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increasing the force that increasing the force that can be applied to an can be applied to an object. (car jack)object. (car jack)

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increasing the increasing the distance over distance over which the force which the force can be applied. can be applied. (ramp)(ramp)

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by changing the by changing the direction of the applied direction of the applied force. (opening the force. (opening the blinds)blinds)

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increasing the speed in increasing the speed in which the work is done.which the work is done.

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Six Simple MachinesSix Simple Machines

The six simple machines are:The six simple machines are: Lever Lever Wheel and Axle Wheel and Axle Pulley Pulley Inclined Plane Inclined Plane Wedge Wedge Screw Screw

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Forces involved:Forces involved:

Input Force Input Force FFII

Force Force applied applied toto a machinea machine

Output Output ForceForce FFOO

Force Force applied applied byby a machinea machine

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Two forces, thus two types of Two forces, thus two types of workwork

Work InputWork Input work done work done onon a a

machinemachine

=Input force x the =Input force x the distance through distance through which that force which that force acts (input acts (input distance)distance)

Work OutputWork Output Work done Work done byby a a

machinemachine

=Output force x =Output force x the distance the distance through which the through which the resistance moves resistance moves (output distance)(output distance)

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Can you get more work out than Can you get more work out than you put in?you put in?

Work output can never be greater Work output can never be greater than work input.than work input.

Ideal machineIdeal machine WWinin = W = Woutout

100% energy transfer.100% energy transfer.

There is no such thing as an There is no such thing as an ideal machine – you always ideal machine – you always lose some energy (through lose some energy (through friction, air resistance, etc.)friction, air resistance, etc.)

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Efficiency – a measure of Efficiency – a measure of how much of the work put how much of the work put into a machine is changed into a machine is changed into useful output work by into useful output work by the machine. (less heat the machine. (less heat from friction)from friction)

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efficiency = efficiency =

(W(Woutout / W / Win in ) x 100%) x 100%

WWinin is always is always

greater than Wgreater than Woutout

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Mechanical Advantage Mechanical Advantage How much a machine How much a machine

multiplies force or distancemultiplies force or distance

output force (Foutput force (FRR)) MA = input force (FMA = input force (FEE))

OrOr

input distanceinput distance

output distanceoutput distanceCopy this

The LeverThe Lever

A bar that is free to pivot, or move A bar that is free to pivot, or move about a fixed point when an input about a fixed point when an input force is applied.force is applied.

FulcrumFulcrum = the pivot point of a lever. = the pivot point of a lever. There are three classes of levers There are three classes of levers

based on the positioning of the effort based on the positioning of the effort force, resistance force, and fulcrum.force, resistance force, and fulcrum.

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LeverLeverMA = MA = Length of effort armLength of effort arm

Length of resistance Length of resistance armarm

Remember that Length is the same as distanceRemember that Length is the same as distance

oror

input distanceinput distance

output distanceoutput distance

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INPUT FORCE (EFFORT FORCE)

OUTPUT FORCE (Resistance Force)

INPUT ARM (EFFORT DISTANCE)OUTPUT ARM

(RESISTANCE DISTANCE)

FULCRUM

Inclined PlanesInclined Planes

Imagine how hard it would be to walk up the side Imagine how hard it would be to walk up the side of a steep hill. of a steep hill.

It would be MUCH easier to follow a gentle slope It would be MUCH easier to follow a gentle slope of a winding trail….why is this?of a winding trail….why is this?

What is happening to input distance if you decide to take the curvy trail instead of going straight up the hill?

Because input distance is greater than output distance, in this case, the input force is decreased…..so it’s easier for you!

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Inclined Inclined PlanePlaneMA = MA =

effort distance effort distance

Resistance distanceResistance distance

ororinput distanceinput distance

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Inclined PlanesInclined Planes

Inclined plane: a slanted surface Inclined plane: a slanted surface along which a force moves an object along which a force moves an object to a different elevationto a different elevation

Input distanceOutput distance

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Inclined PlanesInclined Planes

What is the MA of the following What is the MA of the following inclined plane?inclined plane?

6m1 m

Mechanical Advantage = 6

MA for inclined plane will NEVER be less than 1

WedgesWedges

Similar to inclined planes BUT sloping Similar to inclined planes BUT sloping surfaces can move.surfaces can move.

Wedge: a V-shaped object whose Wedge: a V-shaped object whose sides are two inclined planes sloped sides are two inclined planes sloped toward each other.toward each other.

Examples: knife, axe, razor blade

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The ScrewThe Screw

An inclined plane An inclined plane wrapped around a wrapped around a cylinder.cylinder.

The closer the The closer the threads, the threads, the greater the greater the mechanical mechanical advantageadvantage

Examples: bolts, Examples: bolts, augers, drill bitsaugers, drill bits

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The PulleyThe Pulley

A chain, belt , or A chain, belt , or rope wrapped rope wrapped around a wheel.around a wheel.

Can either change Can either change the direction or the the direction or the amount of effort amount of effort forceforce

Ex. Flag pole, Ex. Flag pole, blinds, stage blinds, stage curtaincurtain

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PullePulleyy The MA of a pulley or pulley system The MA of a pulley or pulley system

is equal to the number of pulleys is equal to the number of pulleys supporting the load being lifted.supporting the load being lifted.

A single fixed pulley only changes A single fixed pulley only changes the direction so MA = 1the direction so MA = 1

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MA = Count # of pulleys in a rowMA = Count # of pulleys in a row

Fe

Wheel & AxleWheel & Axle

Consists of 2 discs or cylinders, each Consists of 2 discs or cylinders, each one with a different radius.one with a different radius.

wheel

axle

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A combination of two or more simple A combination of two or more simple machines.machines.

Cannot get more work out of a Cannot get more work out of a compound machine than is put in.compound machine than is put in.

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Rube Goldberg MachinesRube Goldberg Machines

Rube Goldberg machines are Rube Goldberg machines are examples of examples of complex complex machinesmachines..

All complex machines are All complex machines are made up of combinations of made up of combinations of simple machinessimple machines..

Rube Goldberg machines are Rube Goldberg machines are usually a complicated usually a complicated combination of simple combination of simple machines.machines.

By studying the components By studying the components of Rube Goldberg machines, of Rube Goldberg machines, we learn more about simple we learn more about simple machinesmachines

When you slip on ice, your foot kicks paddle (A), lowering finger (B), snapping turtle (C) extends neck to bite finger, opening ice tongs (D) and dropping pillow (E), thus allowing you to fall on something soft.

Safety Device for Walking on Icy Pavements