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Projectile Force Composition Help

  1. Aug 22, 2006 #1
    Me and my dad got in the follwoing debate: if two identical bullets collide in identical conditions, would they staick together, or be rejected parabolically back.


    Two projectiles of identical dimensions and characteristics collide in identical angles, velocities and directions. There is no atmospherical friction, they are not past terminal velocity, they have no angle (they hit eachother at an angle of zero...so they're shot oblically) and they collide fully head-on.

    How do the resultant forces resolve?

    We understand that there will be one resultant force for object 1 equal to the resultant force ofr object two. Both will be reactions to the orriginal inertia...but will the two forces combine to form one universal resultant with a magnitude of zero or will they each affect their object, bouncing it back?

    :D Plz help.


    p.s. not necessarily important, so no life threatening. :D
  2. jcsd
  3. Aug 23, 2006 #2


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    I would say "C"; none of the above. With the volocities and the materials you're dealing with in most bullets, they'd fragment on impact and fly apart. Most of the pieces would travel away from the impact tightly clustered around the plane that passes through the point where they collide, and is orthagonal to the line along which they were travelling.
  4. Aug 23, 2006 #3
    *poof* there was no spoon
    Last edited: Aug 23, 2006
  5. Aug 23, 2006 #4
    Ouch! Evrika...they break into pieces. Thank you...that seems like a reasonable explanation...:D

    We both (me and my dad) accept it which is rare.
  6. Aug 24, 2006 #5


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    The answer can be quite complicated, since it depends largely on the material properties of the projectiles. They could fragment as lurch describes. However if they are strong enough to avoid breaking up, they would recoil in opposite directions from the point of impact. Another (unlikely) possibility is that they would stick together - but this would require a soft material, unusual for bullets.
  7. Aug 24, 2006 #6
    It all comes down to the properties of the material the bullets are made from.

    At such high speed, they have significant energy.

    A) If it behaves in a "brittle" fashion, LURCH would be correct.

    B) If it has elastic properties (which many metals do), they might translate (some) of their kinetic energy into PE(elastic), as mathman suggested.

    C) If "soft", they may meld together, as mathman also considered.

    Given the "freakish" condition of meeting exactly head on, and that lead is a soft metal, I honestly consider that (C) is a very real possibilty, but given the likelihood of minute differences between the bullets causing non-indentical deformation patterns, it is likely that at least some material will scatter, somewhat along the lines of (A).

    Does lead have ANY elasticity? I don't know, but even if it did, the results of (C) would probably mean the bullets became more or less fused into one contiguous mass (except for the bits that scattered), so any effect of (B) would simply be in this "mess" expanding slightly once KE was completely exhausted; they would not likely bounce apart, then.
  8. Aug 24, 2006 #7
    Exactly. You must consider the coefficient of restitution (i.e. measure of elasticity/plasticity of a material)
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