Elastic collision?

[Physics is Phun]

Is elastic collision defined as a collision where no energy is lost or where no momentum is lost? We had to do a lab in class and one question was whether the collison was elastic. I think we all got it wrong because we sayed it was elastic because momemtum was conserved. But we were supposed to check if energy was (apparently it wasn't) conserved. (It seems kind of stupid because nowhere in the lab did we have to find the energy so we would have to find it separately to find whether it was elastic or not.) So is elasticity defined by momentum or energy?

[Doc Al]

An elastic collision is one in which the kinetic energy is conserved. Momentum is conserved in any collision, whether elastic or inelastic.

[Tide]

An elastic collision is one in which the internal energy of the colliding objects remains unchanged meaning that the translational plus rotational energy of both objects is conserved.

Also, you were in fact asked in the lab to find the energy when the question of whether the collision is elastic was raised. :-)

[Hyperreality]

If you want to know more about inelastic collision, I suggest you look up on Newton's Law of Restitution.