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Perpetual motion machine (view source)
Revision as of 23:14, January 1, 2007
, 23:14, January 1, 2007Sorry, that's not what the phrase "perpetual motion" means
Those who deny that entropy is always increasing, even in closed (and isolated) systems, are left without a persuasive argument that perpetual motion machines are impossible.
Those who deny that entropy is always increasing, even in closed (and isolated) systems, are left without a persuasive argument that perpetual motion machines are impossible.
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This is not the usual meaning of the term "perpetual motion."
:The perpetual motion, then, which has been the subject of such anxious and laborious search, is not a mere motion which is continued indefinitely. If it were, the diurnal and annual motion of the earth, and the corresponding motions of the other planets and satellites in the solar system, as well as the rotation of the sun upon its axis, would be all perpetual motions.
::—Dionysis Lardner, 1857, ''Natural Philosophy for Schools,'' [http://books.google.com/books?vid=OCLC34136808&id=ZzsDAAAAQAAJ&pg=RA1-PA70&lpg=RA1-PA70&dq=%22perpetual+motion%22&as_brr=1 p. 70]
:Perpetual motion is of course possible, as is stated in the first law of motion, "Motion continues in a straight line undiminished in velocity unless acted on by some external force." A top set spinning under conditions where there is no friction will never cease to spin. These conditions are very nearly realized in the motions of the planets and stars. The statement that energy cannot be destroyed asserts this possibility.
:But by "perpetual motion" is generally meant a machine which will do work and keep going though energy equivalent to the work done is not supplied to it. Many attempts have been made to construct such a machine. They have all failed. The statement that energy cannot be created denies the possibility of such a machine.
::—S. Lawrence Bigelow (1912), "Theoretical and Physical Chemistry," [Theoretical and Physical Chemistry By S Lawrence Bigelow p. 26]