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Calculation impact force of a bullet of an object

  1. Jan 3, 2013 #1
    I been looking on google and getting help from several people who are trying to help me, but I just can't understand this. It is to advance for me as of now and I need a example to help show me. But I need this for homework so can someone help and provide formula explaining how this would. Be very appreciated.

    This is a complete homemade thing so... bear with me.

    I am trying to calculate the impact force or stopping power (not sure what to call it) or a bullet on an object. I need a function cause variables will be changing nothing is a set one.

    Variables:
    Mass of bullet
    Mass of Object
    Air Resistance
    Velocity
    Force (F=MA)
    Bullet Weight
    Diameter of bullet (If that has any effect or usefulness)
    Density of Object (If that has any effect or usefulness)


    I've tried making a custom equation, but I was told I just made it so stuff would cancel each other else cause I was thinking what would be a positive effect and offsetting it by a negative effect.

    Any how would really be nice. Spent many hours on trying to get this to be as realistic as possible.
     
  2. jcsd
  3. Jan 3, 2013 #2

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Knowing the mass and velocity of a bullet, you know its kinetic energy and so, in order to stop it, the object must do that amount of work on it. But that is energy, not force. There is a "conservation of energy" law, NOT "conservation of force". If you know the distance the bullet penetrates, then you could calculate the (average) stopping force by "work equals force times distance".
     
  4. Jan 3, 2013 #3
    In order to do this right, you need to take into account the mechanical deformation behavior of the body that the projectile is hitting. Certainly, hitting a steel object will be different than hitting a more compliant object, such as a very viscous liquid contained in a thin plastic pouch. You will have to solve the dynamic stress-equilibrium equations for the object, which is a set of non-linear partial differential equations. In practice, this would involve the use of finite element software. I'm not saying that this problem can't be done, but I do think you are underestimating its complexity. (You would also have to take into consideration the plastic deformation of the projectile).
     
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