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

Inelastic Equations

  1. Jun 27, 2008 #1
    Hey guys, Ive been having a nasty problem in the construction of my physics engine, and it goes as follows.

    When I have the mass and initial velocity of two objects (and Ill assume its a head on collision to simplify matters), how would you calculate the final velocity of both objects, when your given the fact that the collision is only a certain degree elastic, for example, one collision may only be 80% elastic, the other 20% of the energy is converted into heat.

    Any help would be greatly appreciated.
  2. jcsd
  3. Jun 27, 2008 #2
    Oh and after reviewing the Guidelines, should this be in the "Homework" type of area (even though it isn't related to schoolwork)?

    If this is the wrong place, Ill move it as soon as I can figure out how.
    Last edited: Jun 27, 2008
  4. Jun 27, 2008 #3


    User Avatar
    Homework Helper

    Well the coefficient of restitution would help....

    [tex]e= \frac{v_2-v_1}{u_2-u_1}[/tex]
  5. Jun 28, 2008 #4
    So how would I use this coefficient? And does it change or become altered if the masses of the objects is different? Ill try sub-ing it in to a few equations and see if theres a viable solution. Thank you for you help.

    EDIT: I'm still having difficulties. After subbing that coefficient into the momentum formula and simplifying, I cannot get a viable answer. Was placing it in the momentum formula the wrong step?
    Last edited: Jun 28, 2008
  6. Jun 28, 2008 #5


    User Avatar
    Homework Helper

    Read down the wikipedia page for http://en.wikipedia.org/wiki/Coefficient_of_restitution" [Broken], it has a formula for the final velocity. But you'd need to knwo the value of the COF and the inital velocities.
    Last edited by a moderator: May 3, 2017
  7. Jun 28, 2008 #6
    Ah okay, Ive got it now.

    Thank you for you help, I believe in my equations I had the system of equations as

    V2 = CR(U2-U1) + V1

    Where the in the brackets the It is actually (U1-U2).

  8. Jun 28, 2008 #7


    User Avatar
    Homework Helper

    Yeah it's supposed to be U1-U2, my mistake,it's the ratio of the of the relative velocities.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook