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

Acceleration due to air resistance?

  1. Feb 23, 2007 #1
    a friend of mine asked if i could help him work out some equations for a (fairly) long range projectile, to go no farther than 2 miles or so. i have everything reasonably worked out except for acceleration due to air resistance. i'm using the equation from https://www.physicsforums.com/showthread.php?t=9066" thread to calculade Fd, and Cd=.295, rho=1.22752kg/m^3, A=pi.2^2m^2, v=240m/s, firing an object with a mass of .23kg. (Cd and rho both came from the Nasa website) I did the calculations and got an estimated acceleration of about (-)5698 m/s^2, which obviously cannot be right.

    I was also wondering if there is any way to get a more accurate velocity by factoring in acceleration of gravity and air resistance. I'd assume it'll take some nasty algebra/calculus, but i can't figure it out on my own.

    any help is greatly appreciated.
    Last edited by a moderator: Apr 22, 2017
  2. jcsd
  3. Feb 24, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper

    Area = 4pi square meters and a mass of only 0.23 kg? That sounds pretty much like a 2 meter diameter balloon to me.

    If you tried moving something as big and light as that at 240 m/s (mach 0.7), the deceleration would indeed be large.
    Last edited: Feb 24, 2007
  4. Feb 24, 2007 #3


    User Avatar

    I think the area is 0.04pi m^2. Still very large. A projectile with a 20 cm diameter with a mass of only 0.23 kg canĀ“t fly at 240 m/s.
  5. Feb 24, 2007 #4
    Its not a wieldy problem, first Cd is not a constant at all but varies with velocity in a complex fashion, making this impossible to find an exact closed form solution. However, you could approximate a soln using a fixed Cd and initial V thats only subject to drag and gravity. But check the diameter, this is as pointed out much too low a ballistic coefficient to go anywhere due to whiffle ball effect.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook