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

Fluid/Air Friction

  1. Sep 2, 2006 #1
    I'm trying to figure out the trajectory of a ball but i don't know how to incorporate air friction. I've googled it several times but havn't found anything. Most are just examples but don't describe how to calculate it.
  2. jcsd
  3. Sep 2, 2006 #2
    If you have all the forces on the ball, including friction, you can find the net force on it and use that to determine its trajectory. Pretty simple really.
  4. Sep 2, 2006 #3
    Well, i got the trajectory of the ball without friction already, but i don't know how to add fluid friction simply because i don't know how to calculate it. Is there some kind of formula for fluid friction?
  5. Sep 2, 2006 #4


    User Avatar
    Staff Emeritus
    Science Advisor

  6. Sep 2, 2006 #5
    So...drag equation is:
    D = Cd * r * .5 * V^2 * A
    Cd = Drag Coefficient
    r = air density
    V = velocity
    A = reference area

    To find the drag coefficient, the only thing it describes "The drag coefficient is a number that aerodynamicists use to model all of the complex dependencies of shape, inclination, and flow conditions on aircraft drag."

    So i'm now confused on how to get the drag coefficient.
  7. Sep 2, 2006 #6


    User Avatar
    Staff Emeritus
    Science Advisor

    Drag coefficients are determined experimentally, and for some common shapes, e.g. a ball or sphere, the drag coefficient may be tabulated and available from a report or textbook.
  8. Sep 2, 2006 #7
    Lump all the terms into one 'constant' - you can compute it more accurately later, then you have a relationship in v^2... Work this back into your equation/s of motion & you should be well on your way...

  9. Sep 3, 2006 #8


    User Avatar
    Homework Helper

    The direction of the drag opposes the motion of the ball. That is it will be in the opposite direction of the velocity of the ball. Are you trying to solve it numerically or analytically?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook