Momentum conservation

If a ball bounces on an object with a velocity V and then rebounds with a velocity of -V then its momentum has changed from +P to -P. How can this abide to the conservation of momentum?

Reply 1

Joinedup

Original post by JakeRStudent

If a ball bounces on an object with a velocity V and then rebounds with a velocity of -V then its momentum has changed from +P to -P. How can this abide to the conservation of momentum?

You've got to be somewhat careful about what you consider as being part of the system in which momentum is being conserved... the object the ball is bouncing off has mass and is subject to an impulse during the collision - so it's changing momentum too even if you can't notice any change in it's velocity.

Reply 2

JakeRStudent

Original post by Joinedup

Ah I think I see. So considering the total momentum before must be equal to the total momentum aftef would the walls momentum be equal to 2mV after the collision?

Reply 3

mik1a

Original post by JakeRStudent

Ah I think I see. So considering the total momentum before must be equal to the total momentum aftef would the walls momentum be equal to 2mV after the collision?

That's right. You just don't notice the wall moving down because it's connected to the planet.

Reply 4

Joinedup

Original post by JakeRStudent

Ah I think I see. So considering the total momentum before must be equal to the total momentum aftef would the walls momentum be equal to 2mV after the collision?