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Burning question:

  1. Jan 18, 2008 #1
    Please note that this is something that has been eating me lately...it is in EVERY way unrealistic. Keep that in mind, before saying "But ogregun, that is not at all possible", because I understand this already. Thanks. And now....

    The scenario is that you have something that is shaped similar to a domino. It is 10 light years (!) tall. It is standing on a flat surface...that has the same gravitational rules as earth, (actually its entire body of existence is abiding by these physics). It then gets a nudge the equivalent in impact/velocity of a normal finger nudge with a normal sized domino.

    What happens?

    The first thing I'm wondering is how long would it take to reach impact? Would it take the same amount of time as a normal sized domino? I'm thinking it would but I'm not sure.

    I'm also wondering what rate torwards the surface it would be travelling once it reached full speed...would it be travelling faster than light? By my thinking it would hit the ground as fast as a normal domino (same gravity, same equivalent impact to send it down). If this is the case, and it takes less than a second for a 10 light year tall object to travel to the ground...wouldn't it be travelling faster than light?

    Thanks in advance for awnsers. :)
  2. jcsd
  3. Jan 18, 2008 #2


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    Staff: Mentor

    Calculating how long it takes a stiff object to fall is actually a common basic dynamics problem. It is a function of the height of the object alone (assuming it is uniform density). But there's a problem - the taller the object, the greater the forces trying to break it apart. There are some neat videos on the net of tall towers being toppled. The difference in acceleration along the length of the tower causes a large force that breaks it apart, with the different parts then falling approximately at g.

    But, you say, what if it was infinitely stiff? What if pigs could fly? They can't. Regardless, when you attempt to accelerate any object to a high fraction of the speed of light, Relativity takes over and prevents you from achieving the speed of light.
    Last edited: Jan 18, 2008
  4. Jan 18, 2008 #3
    If you scaled a domino up to 10 light-years, it would not fall to earth (much); earth would fall to it.
  5. Jan 19, 2008 #4


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    Gold Member

    Think of it as being similar to a weight on the end of a string, being swung around you. The rpm's are practically limited only by your muscles, how much you can spin around without passing out, and the strength of the string; there's no way that you could attain relativistic speed on the weight. Theoretically, though, the limit is when the speed of the weight approaches c. If you were to get to that limit, and then let the string out, the weight would not speed up. On the contrary, its angular speed would slow down since it would have farther to go for each degree of movement at the same speed. Similarly, your rigid domino could not fall at an angular speed that allowed the far end to reach c.
    Also, the toppling force would propogate through the domino at the speed of sound in that material, not instantly.
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