# Elastic relativistic collisions

1. Jul 29, 2006

### Amith2006

# In a perfectly elastic relativistic collision, which one of the following quantities is not conserved:
a)Momentum
b)Energy
c)Rest mass
d)Angular momentum
In non relativistic elastic collisions, energy and momentum will be conserved. But I don’t know about relativistic elastic collisions. Could anyone please clear my doubt? Can we apply the Newtonian concepts in these cases? Suppose the collision is inelastic (relativistic), then which quantity will be conserved?

2. Jul 29, 2006

### quasar987

I'm puzzled. As far as I know, there is no way to prove conservation of momentum. However, experiments confirm that relativistic momentum is conserved in inelastic collisions (such as particle collisions). Rest mass is conserved by definition of an inelastic collision. Energy is $\sqrt{p^2c^2+m^2c^4}$ so it is conserved since p and m are. Regarding the angular momentum, if you take the coordinate system in which the collision is monitored to have its origin at the point of collision, then angular momentum before and after the collision are 0. So, angular momentum is conserved too.