| MadSci Network: Physics |
Hello, Dean! According to general relativity, there really is no such condition as "not moving." You may say to yourself "but the chair I'm sitting upon isn't moving." From your perspective, it isn't. But to a space shuttle astronaut, your chair is moving at Mach 25, and the chair the astronaut is sitting on is not moving. Hence the name "relativity" - everything is relative to the speed and direction of the observer. Since general relativity recognizes no fixed point of reference, everything in the universe can be considered moving. Therefore, gravity can't really be said to start affecting objects. It's always affecting them, and always has, and always will. A good way to visualize the curvature of space is to imagine a bedsheet being pulled tight at each corner. The bedsheet is flat. But if we place a tennis ball on it, the sheet now has a depression in it. The nearer we are to the tennis ball, the less flat the bedsheet is. Our flat bedsheet has become curved by the presence of mass. A billard ball produces more curvature than a tennis ball, and a person standing on the sheet would curve it greatly. Two bowling balls on the sheet would roll toward each other. They are each being affected by the curvature of space caused by the mass of the other bowling ball. In our bedsheet example we have friction, which would slow the movement of the balls. Friction isn't a significant factor in space, so there really isn't any stay-where-you-are tendency to be overcome. Dis goed om a vra van 'n Suid Afrikaner te antwoord. Ek het in Johannesburg vur twee jaare gebly. Maar almaal het vur my English gepraat, dus my Afrikaans is nie goed nie. I hope this answers your question. Layne Johnson
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