# Collision -- why there is no parallel component?

1. Jul 16, 2014

### Jzhang27143

say that a particle collides elastically with a wall 60 degrees from the wall's normal. the force from the wall is along the wall's normal. My questions is why there is no parallel component to the force from the wall since the particles velocity had a parallel component.

2. Jul 16, 2014

### elegysix

there will be a parallel component to the force on the ball/particle unless you're assuming a frictionless wall. In beginning physics this is usually ignored because it is a minor effect. This is easily verifiable - when you throw a ball and it bounces, it will spin. The spinning is caused by the parallel component of the force on the ball.

If you're talking solid state / particles / lattice interactions, that is beyond me.

3. Jul 16, 2014

### Delta²

There is parallel component but is being neglected.

4. Jul 16, 2014

### paban142

yes there is parallel componet but is being neglected , if you imagine a stretched wall or the collision may be with a giant rock then we can understand

5. Jul 17, 2014

### sophiecentaur

We take things a step at a time. Start with the most ideal case and work upwards - or leave it at that, if you want to. Even the coefficient of restitution, beloved of all students, is only an approximation but it does well in many cases.

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