# linear momentum, collisions, and friction

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just a simple question, when two objects collide horizontally is any friction involved? to me if there is a collision on the bottom of the object the force of friction should be applied only to the x axis velocity of that object and if the object collides on say the right side then only the objects velocity on the y axis is effected? is this assumption true? or does friction slow an object down on a straight on collision also?

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Friction is always 'involved' when non-smooth surfaces come into contact, but I'll assume you're asking if any energy is lost to it.

The answer depends on the velocities, shapes, materials and coefficients of restitution of the objects. If any point on the surface of one of the objects makes contact with more than one continuous point on the other (this could occur for a few different reasons) during the course of the collision, then energy will be lost to friction.
If the objects, however, rebound without 'slipping' against one another then no frictional forces will perform any work on the bodies.
Of course, I use the term 'friction' quite strictly - energy will almost certainly be lost to a variety of different resistive forces, but friction in the physical sense wouldn't be one of these.

I guess the short answer is 'no'.

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