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

MachinesMachines

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

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

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

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

Work InWork In

Effort force – FEffort force – FEE (Force in)(Force in)

The force applied to the The force applied to the

machine (usually by you)machine (usually by you)

Work in – WWork in – Winin (Force in x distance in)(Force in x distance in)

The work done by you on theThe work done by you on the

machine machine

Work OutWork OutResistance force – FResistance force – FRR (Force out)(Force out)

The force applied by the The force applied by the

machine to overcome machine to overcome resistanceresistance

Work out – WWork out – Wout out

(Force out x distance out)(Force out x distance out)

The work done The work done

by the machine by the machine

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.)

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)

efficiency = efficiency =

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

WWinin is always is always

greater than Wgreater than Woutout

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 distance

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

LLEE

LLRR

Inclined Inclined PlanePlaneMA = MA =

effort distance effort distance

Resistance distanceResistance distance

ororlength of slopelength of slope oror l l

height of slope height of slope hh

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