1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Velocity vs Acceleration

  1. Sep 7, 2008 #1
    What is the difference between average acceleration and average velocity?
  2. jcsd
  3. Sep 7, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Velocity and acceleration are two different quantities. Velocity is the rate of change of displacement; acceleration is the rate of change of velocity.
  4. Sep 7, 2008 #3
    So can an object have the same average velocity and average acceleration?
  5. Sep 7, 2008 #4


    Staff: Mentor

    No, the units are different. You might have an object with an average velocity of 1 m/s and an average acceleration of 1 m/s², but those are not the same despite both having the number 1. Just like 1 orange is not the same as 1 apple.
  6. Sep 7, 2008 #5
    An athlete starts at point A and runs at a constant speed of 6.0m/s around a round track 100m in diameter. find the x and y components of this runners average velocity and acceleration between points a, b, c, d (equally apart on circle).

    So there is no acceleration because the speed is constant?
  7. Sep 7, 2008 #6


    Staff: Mentor

    Both velocity and acceleration are vector quantities. In other words they have a magnitude and a direction. If you change the direction of your velocity you have accelerated even if you have not changed the magnitude of your velocity (speed).
  8. Sep 7, 2008 #7
    ah....okay I see....thanks, i will start working on this problem!!
  9. Sep 7, 2008 #8
    So...tell can you please tell me if I am on the right track?

    A = (-50, 0) B = (0,50) C = (50, 0) D = (0, -50)

    Circumference = (pi * r^2) = 7854m

    time between points = 7854m / 6.0m/s = 1309 s

    X components:
    Vax, A = (0-50m)/1309s = -0.038 m/s

    Aax, A = (0-50m/s)/1309s = -.038m/s/s
  10. Sep 7, 2008 #9

    Doc Al

    User Avatar

    Staff: Mentor

    Careful: You found the area instead of the circumference.

    Correct this. Also: The points are spaced 1/4 circumference apart.

    To find the average velocity between points A and B, for example, first find the displacement between A and B. (It's a vector that points from A to B.)
  11. Sep 7, 2008 #10
    oops...okay so the circumference is 314m.

    Time between points is 314m / 6.0m/s / 4 13.0s between each section.

    so for A - b

    displacement Ax = (0-50m)/13s = -3.84 m/s
    displacement Ay, A = (50-0)/13s = 3.84 m/s

    VA = sq rt[(-3.84^2)+(3.84^2)] = 5.43 m/s

    Aax = 3.84m/s^2 Aay = -3.84m/s^2
  12. Sep 7, 2008 #11


    User Avatar
    Homework Helper

    Hi nwells1998,

    I don't believe this is right for the displacement, even though some of your numbers are right. Let's say point A is 50m to the west of the circle and point B is 50 m to the north of the circle. To find the displacement, you need to know how far B is from A, and also what direction B is from A. What would those answers be?

    Then the average velocity is found from:

    average velocity = displacement / time

    The average acceleration is (change in velocity)/(change in time). To answer that, you need to know what the velocities are at A and B. What are those?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook