Physical SciencePhysical Science

Ch. 5Ch. 5

WorkWork• The transfer of energy The transfer of energy

that occurs when a force that occurs when a force

makes an object move.makes an object move.

• Motion is in direction of Motion is in direction of

applied force.applied force.

WorkWork

Work = Force*distanceWork = Force*distance

Work is measured in JoulesWork is measured in Joules

Joule is a Newton-meterJoule is a Newton-meter

J = N * mJ = N * m

PowerPower

• The amount of work done The amount of work done

in a certain amount of in a certain amount of

time.time.

• The rate at which work is The rate at which work is

done.done.

PowerPower

Power =Power = workwork = = EnergyEnergy timetime timetime

Power = Power = Force*distanceForce*distance timetime

MachinesMachines• Make work easierMake work easier• Simple machineSimple machine

–Does work in only one Does work in only one directiondirection

• Complex machineComplex machine–Does work in more than one Does work in more than one

directiondirection–Combination of more than Combination of more than

one simple machineone simple machine

Simple MachinesSimple Machines

• Incline PlaneIncline Plane

• WedgeWedge

• ScrewScrew

• LeverLever

• PulleyPulley

• Wheel & AxleWheel & Axle

• Incline PlaneIncline Plane–Sloping surface that reduces the Sloping surface that reduces the

amount of force required to do workamount of force required to do work

• WedgeWedge–An incline plane with sloping sidesAn incline plane with sloping sides

–A moveable incline planeA moveable incline plane

• ScrewScrew–An incline plane wrapped in a spiral An incline plane wrapped in a spiral

around a cylindrical postaround a cylindrical post

• LeverLever–Bar that is free to pivot or turn Bar that is free to pivot or turn

about a fixed pointabout a fixed point

• PulleysPulleys–Grooved wheel with a rope Grooved wheel with a rope

running along the groove.running along the groove.

• Wheel & AxleWheel & Axle–2 wheels of different sizes that 2 wheels of different sizes that

rotate togetherrotate together

• A machine where work A machine where work

input equals to work outputinput equals to work output

–Will never exist because of Will never exist because of

frictionfriction

WWinputinput = W = Woutputoutput

Ideal MachinesIdeal Machines

• Mechanical AdvantageMechanical Advantage–Number of times a machine Number of times a machine

multiplies the effort forcemultiplies the effort force• EfficiencyEfficiency

–Measure of how much the Measure of how much the work input is changed into work input is changed into usefuluseful work output work output

Efficiently = Efficiently = WWoutout x 100% x 100% WWinin