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Zero Acceleration

  1. Oct 21, 2007 #1
    1. The problem statement, all variables and given/known data
    Let c be a path in R^3 with zero acceleration. Prove that c is a straight line or a point.

    2. Relevant equations
    F(c(t)) = ma(t)
    a(t) = c''(t)

    3. The attempt at a solution
    so i know that since the acceleration is zero, the velocity must be constant, and when you integrate a constant, you get a straight line...but how to I prove mathematically that the velocity is constant, because you can't integrate 0dt, as far as I know?
  2. jcsd
  3. Oct 21, 2007 #2


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    The indefinite integral, i.e, the anti-derivative of 0 is, indeed, a constant; that is we have:
  4. Oct 21, 2007 #3
    oh ok, so if I integrate that again I get that c(t) = Ct + D, which fits the general equation for a line

    but then, does that also prove that c(t) could just be a single point?
  5. Oct 21, 2007 #4


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    Indeed, since big C could be..0!
  6. Oct 21, 2007 #5
    oh. duh!
  7. Oct 21, 2007 #6


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    Damn, I hate mixed "physics" and "mathematics" problems! You or whoever set this problem, should know that a "path" DOES NOT HAVE an "acceleration". I expect this problem should be "find the equation of motion of a particle whose trajectory is a given path in R3 with acceleration 0. Show that the path is either a straight line or a point". Then you would begin with [itex]\vec{a}= d\vec{v}/dt=[/itex] and go from there.
    Last edited: Oct 22, 2007
  8. Oct 22, 2007 #7

    Gib Z

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    The easiest way would have been to recognise that acceleration is a vector quantity, it is affected both by direction or magnitude. No acceleration, no change in direction, which means constant gradient. Simple as that.
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