Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Acceleration as a function of position, and velocity.

  1. Feb 20, 2012 #1
    If acceleration is a function of position, can you express velocity as a function of position, or would there have to be a time variable? For example, if F = kx = ma, and v0 is given, then a = (k/m)x, so what would the function for v be?

    I would think that, if you know the acceleration at every point along a given path and you know initial velocity, you would also know velocity at every point as well, without having to know what time is.

    My actual problem is more complicated than a spring, but it comes down to ∫ f(x) d? = ∫ a d? = v, but what would the integral be? dx or dt?

  2. jcsd
  3. Feb 20, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper

    Yes, you can do this. For example you can use the chain rule

    dv/dt = (dv/dx)(dx/dt)

    but dx/dt = v, so

    a = dv/dt = v dv/dx.
  4. Feb 21, 2012 #3

    Ken G

    User Avatar
    Gold Member

    That's correct, if you take what AlephZero said, and write it as 0.5*d(v2)/dx = F(x), then integrate over x, you get the concept of kinetic energy on the RHS and potential energy on the LHS, which lets you figure out v(x) without ever knowing t.
    It's over dt, to get the second integral to =v. But it's not useful, since F is a function of x not t. So get v(x) with conservation of energy, and if you want to know what t is doing, say v(x)=dx/dt so t is the integral of dx/v(x).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook