How much do collisions slow an object?

[malloyd]

Originally Posted by Anthony

It's wrong about that part too; in reality, collision damage to both parties is almost entirely determined by the mass of the smaller object.

Well the total energy available to do damage basically is - wlog you can consider the more massive object (M) initially stationary, call the smaller mass (m), and use the difference in velocities v and determine in an inelastic collision the dissipated energy is 1/2 m v^2 (1-m/(M+m)). Which shows you the mass of the heavier object only matters to how much it [reduces] the total damage - the closer M gets to m, the less total damaging energy there is, going to a limit of half as much energy when they're equal as when M>>m. Given we are talking very approximately here anyway for a damage formula, a possible factor of 2 it pretty minor.

But on the question of which one takes how much of the damage, depends on how the energy gets partitioned between them, and that's a [very complex] problem. It's customary to assume it's equal, but really that only holds when the two objects are made of the same stuff and v is substantially greater than the speed of sound in that material.

From the standpoint of a game though, it is often close to equal, made even closer by taking the square root (damage being sqrt(E) in GURPS), and a lot of the differences between materials are going to be reflected in their having a different DR, which you are presumably going to apply. Might as well call them equal and proportional to sqrt (1/4 mv^2)