Inelastic collision

What’s conserved?

In an inelastic collision:

Momentum is conserved
Kinetic energy is not conserved

What does this mean?

The sum of the individual objects’ momentums before the collision is equal to the sum of their momentums after the collision (no momentum is ‘lost’)
The sum of the individual objects’ kinetic energies before the collision is greater than the sum of their kinetic energies after the collision (some kinetic energy is ‘lost’ to the surroundings, for example as heat or sound)

What happens to the objects?

The velocity of each object is reduced after the collision, but they won’t be swapped.
The total momentum of the two objects will be the same before and after the collision, but the total kinetic energy will be less after the collision than it was before.

How does it differ from an elastic collision?

The key difference is that some energy is lost from the system in an inelastic collision, whereas no energy is lost from the system in an elastic collision.

Perfectly inelastic collisions

In a perfectly inelastic collision, the two objects stick together after the collision, and move together at the same velocity.

That’s only possible though if the larger object is moving faster than (and towards) the smaller object before the collision, so that the smaller object can catch up to the larger object and stick to it.

flashcards

Question	Answer
In an inelastic collision, what is conserved?	[[momentum
In an inelastic collision, how does the total kinetic energy before the collision compare to after?	The sum of kinetic energies before the collision is greater than the sum after the collision.
What happens to the velocity of each object after an inelastic collision?	The velocity of each object is reduced, but they won’t be swapped.
How does an inelastic collision differ from an elastic collision?	In an inelastic collision, some energy is lost from the system; in an elastic collision, no energy is lost.
What defines a perfectly inelastic collision?	The two objects stick together after the collision and move together at the same velocity.
In a perfectly inelastic collision, when is it possible for the objects to stick together?	Only when the larger object is moving faster than (and towards) the smaller object before the collision, so the smaller object can catch up and stick.
After an inelastic collision, what is true about the total momentum and total kinetic energy of the two objects?	Total momentum is the same before and after; total kinetic energy is less after than before.