Problem
Youandafriendarebuildingadoghouse.Thewoodenboardsarecut.Theholesaredrilled.Thereisjustonethinglefttodo.Youhavetoconnecttheboardstotheframe.Yougrabascrewdriver andsomescrews,andgoto work.
Thefirstturnofthescrewiseasy.Butthenitgetshardertoturn.YourdogOllietiltshishead.Hemustbewonderingwhat’sgoingon.Youarewondering, too!
Solution
Yourfriendishavinganeasiertime.Yourscrewdriversarethesamesize.Theholesarethesamesize.Eventhescrewsarethesamesize.Sowhat’sthedifference?Thenyouseeit.Theridges,orthreads, arefartherapartonyourscrews.Yourfriend’sscrewshavealotmorethreads.Andthey arereallyclosetogether.Thatmustbe it!
Youtryoneofyourfriend’sscrews.Youhavetoturnitalotmoretimes.But,theyareeasyturns.Thescrewgoesinfast.“That’smorelikeit!”you say.
It's Simple
Ascrewisasimplemachine. Simplemachineshelpusdowork.Theyhelpmovethingsfaster,farther,or moreeasilythanwecanwithout them.
Simplemachineshaveonlyafewparts.Somearemadeofonlyonepart.Nearlyeverymachineismadeofoneormoresimple machines.
ACloserLook
Ascrewwithfewerthreadsrequiresmoreforcebuttakeslesstimeto move.
more threads
fewer threads
threads
Whenyouturnthescrewdriver,thescrewchangesthedirectionoftheforce,soitgoesforwardintothe wood.
TheTurnoftheScrew
Ridges,orthreads,wraparoundascrew.Theyformaramp.That’swhatmakesascrewdoits job.
Trytwistingascrewintoapieceofwood.Putthetipofascrewdriverintotheslitontopofthescrew.Turnthehandle.Thattakessomeeffort.Thiseffortprovidesthe forcethatdrivesthescrewintothe wood.
Eachturndirectstheforceinacircle.Thescrewchangesthedirectionsoftheforce.Thescrewmovesinacircle.Theforcedrivesthescrewdownintothe wood.
A screwwith22threadsmeans22turnsandneedslessforcetomove.Ascrewwith11threadsmeansonly11turnsbutneedsmoreforcetoscrewintothe wood.