Do kinetic energy conserved in a 2 dimensional collision?

[mentoz]

Like the tittle suggests, do kinetic energy conserved in a 2 dimensional collision? Like when 2 metal balls collide. Thanks!

 

[Vorde]

Sometimes, when this happens we call it an elastic collision:
http://en.wikipedia.org/wiki/Elastic_collision

Sometimes, though, this does not happen. In these cases we call the collision an inelastic collision:
http://en.wikipedia.org/wiki/Inelastic_collision

Nothing is ever perfectly elastic, because kinetic energy is not a conserved quantity, but there are lots of examples where, for all intents and purposes, kinetic energy is conserved. Two metal balls would be a good example of this, and the classic example are billiard balls. How elastic or inelastic a collision is depends primarily on the rigidity of the materials the objects are made from.