# Coefficient of restitution factors

1. May 1, 2010

### DV10

1. The problem statement, all variables and given/known data

On what all factors does coefficient of restitution depend?i mean do we have 1 for a pair of surfaces in contact or a surface has one irrespective of the surface of the other colliding body?Also,practically,does coefficient of restitution change/vary?If yes,could anyone please
specify the dependency on various factors?Lastly,taking the example of a ball and the floor,lets say if I keep dropping the ball on the floor in simultaneous but "different"(ie i let the ball bounce only once)experiments,will the coefficient of resitution reamain same for all experiments(practically and considering a very large number,say of the order of 10 to the power 100 or so,of the same experiment,ie letting the ball bounce once after dropping it from the same height)
2. Relevant equations

e=(v2-v1)/(u2-u1)

3. The attempt at a solution

couldnt infer much from the eqn given above..

2. May 1, 2010

### jtyler05si

From what I have experienced they either gave me the coefficient for the particular case and asked me to find a velocity in some direction and/or at a certain time; or they gave me information and asked me to find the coefficient.

So given that I think the coefficient of restitution is entirely based off of recorded velocity results between two materials/objects. Much like friction coefficients, it is based off of what is making contact with what.
I imagine in the real world you can't assume the coefficient of restitution out of a textbook for a basketball on a wood floor applies to all basketballs. It probably was only applicable to the test ball at a certain pressure, and a million other constraints. It is a good average but if your basketball is just a hair under-pressure it makes a huge difference, we have all seen this.
And for the "simultaneously dropping the balls in different places": I would say it would be the same, IF the balls were the same in the same conditions and hitting the same surfaces with the same conditions. But the answer is no if one is hitting concrete while one is hitting wood, etc.

I hope that helps and I am sure someone will chime in with a much more technical explanation rather than my example driven ramblings.

3. May 1, 2010

### DV10

well what i'm actually looking for is practical variations with conditions.I'm building a project which works on collisions n so i want to know for how long will my original calculations be valid and what all variations will occur with time.still,i appreciate your response.

4. May 2, 2010