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Homework Help: Questions about the formula for acceleration

  1. Sep 25, 2014 #1
    1. The problem statement, all variables and given/known data

    I know that acceleration = change in velocity/change in time. Wouldn’t acceleration therefore also = distance/time2?

    I thought this was true until i learned the formula for motion
    s = distance and u = initial velocity

    Here, if you re-arrange the formula (and assuming that initial velocity =0), a= 2s/t2

    So which of these formulas are right?

    And if i were to create a graph where the slope can help find the acceleration, should i graph 2*distance vs t2 or just distance vs t2?
  2. jcsd
  3. Sep 25, 2014 #2


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    Average acceleration is ##\Delta v / \Delta t##, and average velocity is ##\Delta s / \Delta t##. But ##\Delta v## is not average velocity, so you cannot combine those two equations.
    The SUVAT formula you quote is only valid for constant acceleration.
    Last edited: Sep 25, 2014
  4. Sep 25, 2014 #3


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    Assume constant acceleration, using va for v average:

    v1 = v0 + a Δt
    va = 1/2 (v0 + v1)
    s1 = s0 + va Δt = s0 + 1/2 (v0 + v1) Δt = s0 + 1/2 (v0 + (v0 + a Δt)) Δt = s0 + v0 Δt + 1/2 a Δt^2
  5. Sep 25, 2014 #4
    Acceleration IS equal to distance/time2

    distance = meters (or m)
    time = seconds (s)

    The units for acceleration is: m/s2
  6. Sep 25, 2014 #5
    No, the fact that is has the same units does not mean that they are the same.
    Work is not torque even though both are measured in N*m.

    Acceleration is a measure of change in speed. If the speed is constant, you have no acceleration even if there is some distance traveled in some time.
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