Perpetual Motion

If perpetual motion is theoretically impossible, how is the earth still in orbit? Or how is anything in orbit? There falling at the rate at which the object there falling towards is rotating and they'll never stop rotating or falling so isn't that perpetual motion?

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Plasmana8 years ago
About the magnets, how do they work? And their magnetic field, are they a continuous stream of energy oscillating through the magnets or it is "fortified" energy?
Kiteman9 years ago
All of the orbits we observe are changing, as are the rotational periods.

The Earth's day used to be only 16 hours long, but interactions with the Moon and Sun have slowed us down. Even friction between the oceans' currents and the coastlines is robbing the planet of rotational energy.

The Moon is receding from the Earth at approximately 4cm per year. Earth is receding from the Sun (I forget how quickly). The tiny gravitational twitches inflicted by the planets by each other render orbits chaotic, so that it becomes impossible to predict orbits precisely for more than the next few thousand years.

Looked at on a long enough time-scale, our steady, constant Solar System is, in fact, wildly unstable, with planets and Moons teetering on the cusp of being hurled into the Sun, flung randomly into interstellar space, or smashed haphazardly into each other.
I have just one minor cavil with your discussion. The many-body interactions render the Solar System chaotic on time scales of millions of years, not thousands.

The non-perpetuality of orbits is not dependent upon the bodies' having complex internal structure, as your discussion about tidal friction assumes. A system of two perfect point masses (e.g., two black holes) in orbit has a dipole moment. Consequently, the system will radiate gravitational waves and slowly but surely lose energy, eventually spiralling inward and coalescing.

For a system like the Earth and Moon, the amount of gravitational radiation is immesurably small, and the consequent decay time from this process is probably at least as long as the lifetime of the Solar System, if not the Universe. For a binary pulsar system, that isn't true, and the lifetime is just a few hundred million years.
. "Minor cavil" is redundant. Quibble, quibble, quibble. . But, seriously, thanks for the clarification.
Cool! Have you really been around long enough to be a proper Usenet Grammar Nazi? Oh, look! I just launched a flamewar by bring Hitler into the discussion, just like in the Good Old Days :-)
. ROFLMAO . Actually, Kiteman is The Grammar Nazi (and Master YEC Hunter). Goodhart handles the bad puns (with plenty of help from caitlinsdad). Adrian monk and jessyratfink show us the female perspective. I just stir up hate and discontent.
I beg to differ, my puns are as good as puns can be, although I am not normally into begging ;-)
Oh, I always thought they were good...
as good as puns can be I guess ;-)
if your old and can understand the ;P
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