Thepulleyatthetopofaflagpolestaysinoneplace.It’sattached,orfixed,tothepole.So,it’scalledafixed pulley.

Afixedpulleyisfineforliftingsomethinglikeaflag.Butwhatiftheloadismuchheavier?Whatiftheloadistheengineofacar?Youcouldneverliftitusingonefixed pulley.

So,addasecondpulleybelowthefixedone.Attachthesecondpulleytotheload.Thatway,thepulleymoveswiththeload.Andthesecondpulleydoublesyourforce!It’slikehavingtwopeoplepullinginsteadof one.

Addingathirdpulleymultipliesyourforcebythree.Afourthpulley. . . well,yougettheidea.Thismayseemlikemagic.Butit’sscience.Theropesupportstheloadbyloopingatthebottomofthepulleysthatlift it.

Countthepiecesofropeinthediagram.Thenumberofpiecestellsyouhowmanytimesthosepulleysincreasetheforce.(Countonlythepiecesofropethatloopunderapulley.Theysupportthe load.)

Mostmovablepulleysarejoinedtofixedpulleys.Constructionsitesaregreatforwatchingpulleysin action.

Youknowthatusingmorepulleyswillmultiplyyourforce.Thismeansthatlesseffortisneededfor lifting.

Imagineliftingaheavyboxofbooks.Youuseafixedpulley.Youtakeholdoftheropeandpull.Fourtugslatertheboxisona truck.

Forthenextbox,youaddamovablepulley.Yourforceisdoubled.Yet,youuseonlyhalftheeffort.It’seasier,butittakeseighttugsontherope.That’sthetrade‑off.Themorepulleysyouuse,theeasieritistopulltherope,butthefartheryouhavetopullit.That’sagood trade!