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Dx as change in distance vs dx as infinitesimal x?

  1. Feb 21, 2014 #1
    dx as change in distance vs dx as infinitesimal x???

    Why are they the same notation?

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  2. jcsd
  3. Feb 22, 2014 #2
    Because they're the same thing. What meaning exactly would [itex] dx [/itex] have otherwise?

    If at time [itex] t [/itex] you have some position [itex] x(t) [/itex] then Newton's Law tells you how a small change in position is related to the velocity of the particle - namely [itex] x + dx = x + v(t)dt [/itex], where [itex] v(t) [/itex] satisfies the equation [itex] m\frac{dv}{dt} = F [/itex].
  4. Feb 22, 2014 #3


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    An actual change in distance is often denoted by δx or Δx, to distinguish it from the infinitesimal dx, which is part of Calculus. dy/dx really means the limit of δt/δx as δx approaches zero. In Science, we are often too sloppy about these notations as there may be pitfalls when you don't stick to the 'rules' precisely.
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