# What happens in a collision

1. Mar 9, 2016

### Biker

1. The problem statement, all variables and given/known data
I have a question about this. I will post it once I fully understand my problem with this.

2. Relevant equations
F *t = dp

3. The attempt at a solution
At the beginning i just want to know how a collision happen. So if two object with different velocities collide with each other (They are moving towards each other. Presume that both of them will move in the same direction after the collision.) So of course one of them will lose momentum and the other will gain momentum in that direction.

So my conflict here, Is how long do the forces exert on these objects? so I thought the objects exert these forces on each other because of their tendency to move in their direction. As a result, when the objects have the same velocity in the same direction, they won't have to exert these forces on each other. But this concept is wrong because that doesnt happen in real life. When two objects collide they don't always have the same velocity. So what actually happens?

2. Mar 9, 2016

### SteamKing

Staff Emeritus
For the most part, BOOM!

There are two idealized types of collision, the fully elastic and the fully inelastic. In the fully elastic collision, the two objects bounce off one another without transferring any energy or momentum. In the fully inelastic collision, the two objects merge and stick together, combining their momentum and energy.

http://hyperphysics.phy-astr.gsu.edu/hbase/elacol.html

Actual collisions fall somewhere in between these two ideal cases.

3. Mar 9, 2016

### Biker

I know that and I have solved a lot of questions and problems about that. But I just want to know what actually happens in a collision. How do the forces work here and for how long? Like what makes the objects exert this force and what keeps them from exerting it for a period of time

4. Mar 9, 2016

### SteamKing

Staff Emeritus
Force is not a really useful concept to apply in a collision, except maybe for calculating an impulse, F Δt = m Δv

The two bodies are going to come together, deform a little bit or a lot, depending on how they are constructed, and part of their total energy will be absorbed causing this deformation. Some energy may remain and be available to allow one or both bodies (or parts of same) to move away from the point of collision; or, this energy could be converted to heat or some other form and dissipated, in which case the two bodies will remain in place at the point of collision.

The point is, each collision is different because the characteristics of the colliding bodies are different, their velocities may be different, etc.