MACHINES and MACHINES and EFFICIENCYEFFICIENCYChapter 9.8-9.9

Key TermsKey TermsWork = Force x distanceSimple machine

◦a device used to multiply forces or change the direction of forces

Compound machine◦A machine composed of two or more

simple machines

Key TermsKey TermsInput (effort)

◦Input distance: the distance you input the force when using a machine

◦Input force: the force you use when using a machine

Output (resistance)◦Output distance: the distance the

object that work is done on moves◦Output force: the force required to

move the object without a machine (usually the weight of the object in newtons)

Key TermsKey TermsMechanical Advantage (MA)

◦A unitless ratio that indicates the number of times a machine multiplies your input force

Ideal Mechanical Advantage (IMA)◦The calculated MA, does not consider

frictionActual Mechanical Advantage (AMA)

◦The measured or real MA, does consider friction

Because of friction, AMA < IMA

A simple machineA simple machineMultiplies and redirects forceDoes not reduce the amount of

work to be done, but makes work easier.

MA > 1 means that your input force will be less than your output force

More leverage means more mechanical advantage

If you increase MA, then◦Input force will decrease◦Input distance will increase

Key TermsKey TermsEfficiency (a ratio)

◦Is calculated using the following equations:

◦Actual mechanical advantage/idealized mechanical advantage

◦Useful work output/total work input

Key TermsKey TermsEfficiency of a machine decreases

as friction increases◦Friction increases the thermal energy

by increasing molecular KE (non-mechanical energy)

◦In other words… friction causes the particles to speed up, raising the average KE of the particles (and temperature!)

◦Friction causes the useful work output to be less than the total work input

Key TermsKey TermsWhen using a machine…

◦Work is done to move the object ◦Work is done against frictionUseful work output is the work done to move the object

Total work input is work done to move object + work done against friction

Simple MachinesSimple MachinesTwo families

Lever Inclined plane--Lever

--Pulley

--Wheel and axle

--Ramp

--Wedge

--Screw

fulcrum

The Lever

Three Classes of LeversThree Classes of LeversFirst class

Examples:

Crowbar

See-saw

Three Classes of LeverThree Classes of LeverSecond class

Examples:

Wheelbarrow

Door

Three Classes of LeverThree Classes of LeverThird class

Examples:

Human arm

Baseball bat

Calculating the Mechanical Calculating the Mechanical Advantage of a LeverAdvantage of a LeverMA = input distance/output

distance which is…MA = length of effort arm/length of resistance arm.

Effort armResistance arm

2.5 m

0.5 mEffort or input distance

Resistance or output distance

Calculating the Mechanical Calculating the Mechanical Advantage of a LeverAdvantage of a Lever2nd class lever

3rd class lever

3rd class levers reduce the output force, but increase output distance and speed

2nd class levers decrease the input force but increase the input distance.

Which lever would have the highest mechanical advantage and why?

a

b

cb has the largest input distance, giving the largest MA

PulleyPulley

Fixed pulley

1 support rope

IMA = 1

PulleysPulleys

IMA = 2

Two supporting ropes

PulleysPulleys

IMA = ?

2

PulleyPulleyHow many support ropes?

4

What is the IMA?

4

Wheel and AxleWheel and AxleWheel connected to a shaft

GIVES YOU LEVERAGE

Inclined planesInclined planesRamps

WedgeWedgeTwo inclined planes stuck

together

ScrewScrewAn inclined plane wrapped

around a cylinder

What type of machine is What type of machine is this?this?

Compound: made of two or more machines

Two 1st class levers; two wedges (scissor blades)