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Projectile Physics

  1. Jan 30, 2004 #1
    Ok Guys I need some help here...
    I am in the process of developing my own game and I am trying to think of all the things that I need to consider in order to make the game more realistic. When I am designing the weapons (snipers, grenade launchers, sub machine guns, etc) what are the various things i need to consider in order to get the trajectories and impact results right. For example, consider a bullet from a M4 Carbine of weight 60 grains and a muzzle velocity of 2800 feet/sec. Is there an equation which would define the trajectory that the bullet would follow and could the impact result be reduced to an equation. could this equation consider extreme situations like if the subject would be thrown back by the impact or if it would be a clean exit and what about considering a graze instead of a direct hit.
    Im prolly askin for too much but help me out guys. pweaseeeeeeee :)
     
  2. jcsd
  3. Jan 30, 2004 #2
    They will be able to tell you at the site you goggled this from:

    "from a M4 Carbine of weight 60 grains and a muzzle velocity of 2800 feet/sec."

    I've got friends coming back from Afganistan that will be able to answer your qwestion. If you can wait.
     
  4. Jan 30, 2004 #3
    I think it was quite evident from my original post that I "am trying to make it as realistic as possible". If 2800 feet/sec and 600 grains happen to be the exact specification of a M4 Carbine, maybe it isnt just coincidence? And I seriously doubt anyone from Afghanistan could answer my query. They still havnt mastered speaking english let alone logging onto the internet and posting on a physics forum :)
     
  5. Jan 31, 2004 #4
    I will try to put together an equation for the trajectile.
    [tex]
    y=v_y t- \frac{1}{2}gt^2
    [/tex]
    [tex]
    x=v_xt
    [/tex]
    So,
    [tex]
    t=\frac{x}{v_x}
    [/tex]
    [tex]
    y=v_y (\frac{x}{v_x})- \frac{1}{2}g (\frac{x}{v_x})^2
    [/tex]
    [tex]
    y=f(x)=(\frac{v_y}{v_x})x- (\frac{g}{2v_x})x^2
    [/tex]
    This gives y as a function of x. As you know, this is a parabola.
    I'd like to answer other questions, but don't have enough time now.
     
  6. Jan 31, 2004 #5
    Just to firm what kishtik said:

    The Kinematic equation [tex]s=ut+\frac{1}{2}gt^2[/tex]
     
  7. Jan 31, 2004 #6

    russ_watters

    User Avatar

    Staff: Mentor

    For the purpose of a game, its probably better to reconstruct that using launch angle as your dependent variable in separate x and y equations. The computer can calculate the entire trajectory from the launch angle (and given muzzle velocity) and then move the projectile along that path. See: http://www.rit.edu/~jxa3625/trajectoryreport.htm
     
  8. Feb 4, 2004 #7
    neato... thanks guys... this is a good start... it should be easy to factor in the deceleration due to atmospheric resistance and deviation due to wind using these equations as bases...

    do you guys think it would be possible to vary the damage caused by the projectiles based on impact velocity or would i just be screwing myself trying to implement that? I realize it would surely add to the cool factor of the game physics... but i suppose it would also require greater attention to human anatomy and armour. If nothing else it would be nice to see how intencive the calculations would be on the processor.
     
  9. Feb 5, 2004 #8

    russ_watters

    User Avatar

    Staff: Mentor

    I guess it depends on the type of game, but for most purposes you don't need to bother with those.
    That should work fine - except use kinetic energy, not velocity. Kinetic energy is 1/2 m*v^2.
     
  10. Feb 6, 2004 #9
    actually i am thinking of using Kinetic Power instead of Kinetic Energy since KE does not take into consideration the mass of the projectile.
    [tex]kp=ke\ast m[/tex]
    where, m = momentum.
     
    Last edited: Feb 6, 2004
  11. Feb 7, 2004 #10
    Don't use "grains". Use grams.

    Don't use "feet/second". Use metres/second.

    Don't worry about how much energy you need to get the projectile going. Worry more about the Force with which it hits.
     
  12. Feb 13, 2004 #11
    You can get a free 30 day trial of ballistics software from www.remington.com or www.winchester.com. The tables include the effects of aerodynamic drag, wind drift, temperature and altitude. The coefficient of aerodynamic drag varies greatly with velocity, and is highest near mach 1. I have the calculus formulas and additional information used in these formulas if you need them.
     
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