Why Perpetual Motion Machines Never Work, Despite Centuries of Experiments

Accord­ing to the laws of physics — at least in sim­pli­fied form — an object in motion will stay in motion, at least if no oth­er forces act on it. That’s all well and good in the realm of the­o­ry, but here in the com­plex real­i­ty of Earth, there always seems to be one force or anoth­er get­ting in the way. Not that this has ever com­plete­ly shut down mankind’s desire to build a per­pet­u­al-motion machine. Accord­ing to Google Arts & Cul­ture, that quest dates at least as far back as sev­enth-cen­tu­ry India, where “the math­e­mati­cian Brah­magup­ta, who want­ed to rep­re­sent the cycli­cal and eter­nal motion of the heav­ens, designed an over­bal­anced wheel whose rota­tion was pow­ered by the flow of mer­cury inside its hol­low spokes.”

More wide­ly known is the suc­ces­sor design by Brah­magup­ta’s twelfth-cen­tu­ry coun­try­man and col­league Bhāskara, who “altered the wheel design by giv­ing the hol­low spokes a curved shape, pro­duc­ing an asym­met­ri­cal course in con­stant imbal­ance.” Despite this ren­di­tion’s mem­o­rable ele­gance, it does not, like the ear­li­er over­bal­anced wheel, actu­al­ly keep on turn­ing for­ev­er. To blame are the very same laws of physics that have dogged the sub­se­quent 900 or so years of attempts to build per­pet­u­al-motion machines, which you can see briefly explained in the TED-Ed video above.

“Ideas for per­pet­u­al-motion machines all vio­late one or more fun­da­men­tal laws of ther­mo­dy­nam­ics, the branch of physics that describes the rela­tion­ship between dif­fer­ent forms of ener­gy,” says the nar­ra­tor. The first law holds that “ener­gy can’t be cre­at­ed or destroyed; you can’t get out more ener­gy than you put in.” That alone would put an end to hopes for a “free” ener­gy source of this kind. But even machines that just keep mov­ing by them­selves — much less use­ful, of course, but still sci­en­tif­i­cal­ly earth-shat­ter­ing — would even­tu­al­ly “have to cre­ate some extra ener­gy to nudge the sys­tem past its stop­ping point, break­ing the first law of ther­mo­dy­nam­ics.”

When­ev­er machines seem to over­come this prob­lem, “in real­i­ty, they invari­ably turn out to be draw­ing ener­gy from some exter­nal source.” (Nine­teenth-cen­tu­ry Amer­i­ca seems to have offered end­less oppor­tu­ni­ties for engi­neer­ing char­la­tanism of this kind, whose per­pe­tra­tors made a habit of skip­ping town when­ev­er their trick­ery was revealed, some obtain­ing patents and prof­its all the while). But even if the first law of ther­mo­dy­nam­ics did­n’t apply, there would remain the mat­ter of the sec­ond, which dic­tates that “ener­gy tends to spread out through process­es like fric­tion,” thus “reduc­ing the ener­gy avail­able to move the sys­tem itself, until the machine inevitably stopped.” Hence the aban­don­ment of inter­est in per­pet­u­al motion by such sci­en­tif­ic minds as Galileo and Leonar­do — who must also have under­stood that mankind would nev­er ful­ly relin­quish the dream.

Relat­ed con­tent:

Leonar­do da Vinci’s Ele­gant Design for a Per­pet­u­al Motion Machine

M. C. Escher’s Per­pet­u­al Motion Water­fall Brought to Life: Real or Sleight of Hand?

Leonar­do da Vinci’s Inven­tions Come to Life as Muse­um-Qual­i­ty, Work­able Mod­els: A Swing Bridge, Scythed Char­i­ot, Per­pet­u­al Motion Machine & More

How the Bril­liant Col­ors of Medieval Illu­mi­nat­ed Man­u­scripts Were Made with Alche­my

A Com­plete Dig­i­ti­za­tion of Leonar­do Da Vinci’s Codex Atlanti­cus, the Largest Exist­ing Col­lec­tion of His Draw­ings & Writ­ings

Based in Seoul, Col­in Marshall writes and broad­casts on cities, lan­guage, and cul­ture. His projects include the Sub­stack newslet­ter Books on Cities, the book The State­less City: a Walk through 21st-Cen­tu­ry Los Ange­les and the video series The City in Cin­e­ma. Fol­low him on Twit­ter at @colinmarshall or on Face­book.