About elastic and inelastic collision

[KFC]

I am studying the collision from the text, in which they said inelastic collision is the case when two collide objects stick together after collision. But in the class, the instructor said two objects stuck together is not the sufficient condition for inelastic collision, we should figure out if the kinetic energy conserved or not. So which one is right and why?

 

[Nugatory]

I am studying the collision from the text, in which they said inelastic collision is the case when two collide objects stick together after collision. But in the class, the instructor said two objects stuck together is not the sufficient condition for inelastic collision, we should figure out if the kinetic energy conserved or not. So which one is right and why?

Neither, if you've quoted your instructor correctly (but I'd bet a fair amount that he didn't say "sufficient", he said "necessary", in which case he's right).

An elastic collision conserves kinetic energy; an inelastic collision does not.

If the colliding objects stick together, that's a sufficient but not a necessary condition for the collision to be inelastic.

 

[jtbell]

In other words, if the objects don't stick together, the collision may be either elastic or inelastic, depending on whether KE is conserved or not.

We sometimes call the case where the objects stick together "completely inelastic", and the cases where they don't stick together but KE is not conserved "partially elastic" or "partially inelastic".

 

[KFC]

Thanks guys for your explanation.

 

[PJC01]

Both the text and the instructor are correct in their respective explanations of elastic and inelastic collisions. An inelastic collision is indeed defined as a collision in which two objects stick together after the collision. However, this is not the only criterion for determining if a collision is inelastic.

In an inelastic collision, the kinetic energy of the system is not conserved, meaning that some of the initial kinetic energy is lost during the collision. This can be due to the conversion of kinetic energy into other forms, such as heat or sound, or the deformation of the objects involved.

Therefore, in order to fully determine if a collision is inelastic, we must also consider the conservation of kinetic energy. If the kinetic energy is not conserved, then the collision is considered inelastic, regardless of whether the objects stick together or not.

In summary, both the sticking together of objects and the conservation of kinetic energy are important factors in determining if a collision is elastic or inelastic. It is important to consider both aspects when studying collisions in order to fully understand the dynamics of the system.