Thinkbacktothedifferentkindsofscrewsyouusedtobuildthedoghouse.Eventhoughthescrewswerethesamelength,thethreadsweredifferent.Thescrewswithmorethreadswereeasiertoturn,butyouhadtoturnthemmore often.

That’sthethingaboutasimplemachine:therearealwaystrade‑offs.Themorethreadsascrewhas,thelessforceyouhavetoapply.But,youhavetoapplythatforceoveragreaterdistance.Youmightbethinking,“Whatdistance?Idon’tgoanywherewhenIturnascrewdriver.”Yourbodydoesn’t,butyourhand does.

Thinkaboutthecircleyourhandmakeswhenyouturnthescrewdriver.Ascrewwith30threadsmeans30turnsofthescrewdriver.Stretchoutthoseturns.Addthemup.Nowyoucanseethatyouapplytheturningforceoveradistanceofseveral feet.

Doyouwanttocutdownonthatdistance?Okay,butbepreparedtosupplymoreforcewitheachturn.It’slikemovingastackofbooksfromonedesktoanother.Youcanmovethestackbytakingacouplebooksatatime.Youuselittleforcetopickupthebooks,andyouhavetomakemoretrips.Oryoucanmovethewholestackatonce.Youusealotmoreforce,andit’sonlyonetrip.Ifthewholestackistooheavyortoodangeroustocarry,thenit’sworththeextra trips.

It’sthesamethingwiththescrewwithfewerthreads.Youhavetoputinalotmoreefforttoprovidetheforceittakestoturnthescrew.Maybeit’smoreeffortthanyoucanmuster.Plus,fewerthreadsprovidelessfrictiontoholdthescrewin place.

So,whenitcomestotrade‑offswiththissimplemachine,it’susuallybettertotradedistanceforeffort.Andthat’s notabad trade!

Whenyoudriveascrewintoapieceofwood,thejobiseasierifanarrowholeisalreadythere.That’swhereadrillhelps.Andguesswhat?Adrillbitisa screw.

Amotorspinsthedrillbitquickly.Thetipofthebitispointedsothatiteasilydigsthroughthewood.Inacoupleseconds,youhaveanarrowholethatyoucanmakealittlebiggerwhenyoudrivein the screw.

Largerdrillsmakelargerholesintheground.Somedrillsdigthroughsoilandrocktomakewellsforwateroroil.Otherdrillsmakeholestosetfence posts,telephonepoles,andlight poles.