PulleyPower
Flagpolesusepulleys,too.Thepulleyatthetopstaysinplace.It’scalledafixedpulley.Afixedpulleycanliftsomethinglight.Butwhatifthe loadis heavy?Addasecondpulleybelowthefixedone!Thesecondpulleywilldoubleyour force.
Count thepulleysinthedrawingbelow.Thenumbertellsyouhowmanytimesthosepulleysincreasethe force.
fixed pulley
less
distance,
more
force
greater
distance,
less
force
Afixedpulleychangesthedirectionof force.
Asyouaddmorepulleys,youpulltheropeagreaterdistance.Yet,youuselessforcetomovethe load.
Trade‑offs
Morepulleysmeansthatlesseffortisneededforlifting.Sayyouhadtoliftsomeheavyboxesofbooks.First,youtryafixedpulley.Youtakeholdoftheropeandpull.Fourtugslater,thebox isona truck.
Forthenextbox,youaddasecondpulley.Yourforceisdoubled.Youuseonlyhalftheeffort.It’seasier,butittakeseighttugsonthe rope.
That’sthetrade‑off.Themorepulleysyouuse,theeasieritistopulltherope.Youjusthavetopullit farther.
block
Pulleysusedtogethermakelifting easy.
A blockcontainsseveral pulleys.
blocks
