- #1
walk_w/o_aim
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In explaining why it does not make sense for two objects feeling each other's gravity to simply stay in place, the book "Simple Nature" (Ben Crowell, April 2010 edition) states that:
My question is, why does one planet moving and not the other violate the conservation of energy? I could say that some of the initial gravitational energy between the planets is converted into kinetic energy for only one of the planets. I believe that it can be explained in terms of Newton's action-reaction law, but at this point in the book, forces have not even been discussed yet.
What am I missing here? Any light on the matter would be much appreciated. Thank you.
The Fooites and Barians realize that the gravitational interaction between their planets will cause them to drop together and collide. ... And yet ... maybe they should consider the possibility that the two planets will simply hover in place for some amount of time, because that would satisfy conservation of energy. Now the physical implausibility of the hovering solution becomes even more apparent. Not only does one planet have to “decide” at precisely what microsecond to go ahead and fall, but the other planet has to make the same decision at the same instant, or else conservation of energy will be violated.
My question is, why does one planet moving and not the other violate the conservation of energy? I could say that some of the initial gravitational energy between the planets is converted into kinetic energy for only one of the planets. I believe that it can be explained in terms of Newton's action-reaction law, but at this point in the book, forces have not even been discussed yet.
What am I missing here? Any light on the matter would be much appreciated. Thank you.