Balancedforcesareforcesthatarethesamesizebutworkinoppositedirections.Ifforcesare

Forces

balanced:

•astationaryobjectstaysstationary; • amovingobjectcontinuestomoveatthesamespeed.

Acarormotorbikeusestheenergystoredinfueltomoveatasteadyspeedbecauseitneedsa forcefromtheenginetobalancetheforcesofairresistanceandfriction.

Theamountofairresistanceonsomethingcanbereducedbygivingitasmooth,streamlined shape.Theairresistanceincreasesasthespeedincreases,socarsuseupmorefuelpermilewhen theyaretravellingfast.Airresistanceiscausedbyairparticleshittingthemovingobject.The particlestransferenergytotheobject,whichiswhyobjectsmovingthroughaircangethot.

Pressureonsolids

Pressureistheamountofforcepushingonacertainarea.

Foracertainarea,thebiggertheforce,thebiggerthepressure.Foracertainforce,thebiggerthe area,thesmallerthepressure.

Inthispicture,thethumbisputtingaforceontotheheadofthepin.Theforceis transferredtothepointofthepin.Thepointhasaverysmallarea,sothereisavery largepressureontheboard,andthepingoesin.

Inthispicture,thethumbisputtingaforcedirectlyontheboard.

Theareaofthethumbismuchlargerthantheareaofthepinpoint,sothereisonlya smallpressureontheboard.Thethumbdoesnotgointotheboard.

Magnetsandelectromagnets

Magnetismisanon-contactforce.Amagnetdoesnothavetobetouchingsomethingtoattract

it.Magnetsattractmagneticmaterials.Iron,nickelandcobaltaremagneticmaterials.Mixtures, likesteel,thatincludeamagneticmaterialwillalsobeattractedtoamagnet.Othermetals,such

asaluminiumorcopper,arenotmagneticandwillnotbeattractedtoamagnet.

• Thetwoendsofabarmagnetarecalledthenorth-seekingpoleandthesouth-seekingpole,

ornorthpoleandsouthpoleforshort.

• Anorthpoleandasouthpoleattracteachother.

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• Twonorthpolesortwosouthpolesrepeleachother.

Abarmagnetisapermanentmagnet,becauseitisalwaysmagnetic.Awirewithelectricity flowingthroughithasamagneticfieldaroundit.Anelectromagnetisacoilofwirewithan electriccurrentflowingthroughit.Itisonlymagneticwhilethecurrentisflowing.

Youcanmakeanelectromagnetstrongerby:

• increasingthenumberofcoilsofwire

• increasingthesizeofthecurrent(byincreasingthevoltage)

• usinganironcore.

Magneticfields

Thespacearoundamagnetwhereithasaneffectiscalledits

magneticfield.

Youcanfindtheshapeofthemagneticfieldusingironfilings orusingaplottingcompass.

TheEarthhasamagneticfield.Acompassisasmallmagnet thatwillpointtowardstheEarth’sNorthpole.Butmagnetic materialsplacednearacompasscanchangethedirectionthat thecompasspointstowards.

Levers

Forcescanbeusedtoturnobjectsaroundpivots.Apivotisalso knownasafulcrum.

Leversworkbymagnifyingtheforcethatisputin(theeffort)or they

canmaketheloadmovefurtherthantheeffort.Theamount theforceordistanceismultiplieddependsonthedistances betweentheloadandthepivotandtheeffortandthepivot.

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