Eli5 :How can you generally approximate what the impact forces and time frame of impulse will be in a collision, using both momentum and kinetic energy ?

Question

https://m.youtube.com/watch?v=sCmX5R7KDFM
Expanding on this video, is it proper to think of of KE as a force being applied over a distance, and as thats happening kinetic energy is being lost and it’s being converted into another form of energy , such as heat, sound, elastic potential energy , or plastic deformation. And do you generally need the material densities l/tensile strengths to determine the impact forces and collision time intervals?

In: 0

Answer 1

Depending on your impact, there’s just way too much going on for you to calculate in any straightforward way. If you can get an impact to fit nicely into a specific category, then you will have more luck.

First, what mediates the interaction? Will it be two large flat steel faces? Something soft, like foam or carpet? Something bouncy, like rubber?

If one of these factors sets a limit on your impact characteristics, it makes your job a *lot* easier. One of the easiest examples is a spring-mediated collision. As long as the energy involved is lower than the spring’s maximum stored energy, you can do some simple math to find its maximum compression and from there the time spent traveling that distance.

For another example, a bullet striking a solid steel plate. Lead deforming is pretty much inelastic, so the final forward momentum will be near zero. The bullet will be pretty much pancaked against the target. You know its energy, and you know that the impact cannot take longer than the time it takes for the rear end of the bullet to reach the front of the steel plate. From there you can start putting lower bounds on the force and time.

If inertia and fluid dynamics get involved, then you’re unfortunately stuck with more complicated simulations.