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  • Around 1159 A.D.,

  • a mathematician called Bhaskara the Learned

  • sketched a design for a wheel containing curved reservoirs of mercury.

  • He reasoned that as the wheels spun,

  • the mercury would flow to the bottom of each reservoir,

  • leaving one side of the wheel perpetually heavier than the other.

  • The imbalance would keep the wheel turning forever.

  • Bhaskara's drawing was one of the earliest designs

  • for a perpetual motion machine,

  • a device that can do work indefinitely without any external energy source.

  • Imagine a windmill that produced the breeze it needed to keep rotating.

  • Or a lightbulb whose glow provided its own electricity.

  • These devices have captured many inventors' imaginations

  • because they could transform our relationship with energy.

  • For example, if you could build a perpetual motion machine

  • that included humans as part of its perfectly efficient system,

  • it could sustain life indefinitely.

  • There's just one problem.

  • They don't work.

  • 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.

  • The first law of thermodynamics says that energy can't be created or detroyed.

  • You can't get out more energy than you put in.

  • That rules out a useful perpetual motion machine right away

  • because a machine could only ever produce as much energy as it consumed.

  • There wouldn't be any left over to power a car or charge a phone.

  • But what if you just wanted the machine to keep itself moving?

  • Inventors have proposed plenty of ideas.

  • Several of these have been variations on Bhaskara's over-balanced wheel

  • with rolling balls or weights on swinging arms.

  • None of them work.

  • The moving parts that make one side of the wheel heavier

  • also shift its center of mass downward below the axle.

  • With a low center of mass,

  • the wheel just swings back and forth like a pendulum,

  • then stops.

  • What about a different approach?

  • In the 17th century, Robert Boyle came up with an idea

  • for a self-watering pot.

  • He theorized that capillary action,

  • the attraction between liquids and surfaces

  • that pulls water through thin tubes,

  • might keep the water cycling around the bowl.

  • But if the capillary action is strong enough to overcome gravity

  • and draw the water up,

  • it would also prevent it from falling back into the bowl.

  • Then there are versions with magnets, like this set of ramps.

  • The ball is supposed to be pulled upwards by the magnet at the top,

  • fall back down through the hole,

  • and repeat the cycle.

  • This one fails because like the self-watering pot,

  • the magnet would simply hold the ball at the top.

  • Even if it somehow did keep moving,

  • the magnet's strength would degrade over time

  • and eventually stop working.

  • For each of these machines to keep moving,

  • they'd have to create some extra energy

  • to nudge the system past its stopping point,

  • breaking the first law of thermodynamics.

  • There are ones that seem to keep going,

  • but in reality, they invariably turn out to be drawing energy

  • from some external source.

  • Even if engineers could somehow design a machine

  • that didn't violate the first law of thermodynamics,

  • it still wouldn't work in the real world because of the second law.

  • The second law of thermodynamics

  • tells us that energy tends to spread out through processes like friction.

  • Any real machine would have moving parts

  • or interactions with air or liquid molecules

  • that would generate tiny amounts of friction and heat,

  • even in a vacuum.

  • That heat is energy escaping,

  • and it would keep leeching out,

  • reducing the energy available to move the system itself

  • until the machine inevitably stopped.

  • So far, these two laws of thermodynamics

  • have stymied every idea for perpetual motion

  • and the dreams of perfectly efficient energy generation they imply.

  • Yet it's hard to conclusively say we'll never discover a perpetual motion machine

  • because there's still so much we don't understand about the universe.

  • Perhaps we'll find new exotic forms of matter

  • that'll force us to revisit the laws of thermodynamics.

  • Or maybe there's perpetual motion on tiny quantum scales.

  • What we can be reasonably sure about is that we'll never stop looking.

  • For now, the one thing that seems truly perpetual is our search.

Around 1159 A.D.,

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B1 中級

TED-ED】なぜ永久運動マシンは動かないのか?- ネッタ・シュラム (【TED-Ed】Why don't perpetual motion machines ever work? - Netta Schramm)

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    東東 に公開 2021 年 01 月 14 日
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