# Conservation of momentum & inelastic collisions

## Homework Statement

This question is related to an in-class experiment. The lab involves bouncing a ball and using a motion sensor which creates a graph representing the motion.
The question is: Is the principle of conservation of momentum violated in this collision (the ball colliding with the ground)?

## Homework Equations

m1v1i + m2v2i = m1v1i + m2v2i

## The Attempt at a Solution

I don't think the collision violates the conservation of linear momentum law because the law applies to closed systems, and this system (when the ball collides with the earth) is not closed.
However I'm not sure if my theory on this is correct ...

kuruman
Homework Helper
Gold Member
What does your system consist of? Is it just the ball? What have you learned about momentum conservation, namely when is momentum not conserved?

The experiment only involves bouncing a ball on the ground (and detecting motion). Therefore, I am not sure if the system involves both the ball and the ground, or just the ball.
Regarding momentum, I know that momentum is always conserved in a closed system, but not a system which is affected by external forces.

thanks for helping :)

kuruman
Homework Helper
Gold Member
In a collision there are always at least two parties that participate, an object cannot collide with itself. One party is the ball so it is reasonable to assume that the Earth (or floor which is attached to the Earth) is the other party. Is the Earth-ball a closed system? Are there external forces that affect it?

Okay, so if the system is the earth-ball (and the collision between the two)... I'm not sure if the gravitational force from the earth on the ball is included in the system, or is counted as an external force?

kuruman