Elastic and Inelastic Collisions
Momentum is conserved in every collision, but kinetic energy is conserved only in an elastic one. Adding up the kinetic energy before and after is what sorts one kind from the other.
What a learner can do afterwards
- Applies conservation of momentum in one dimension with signs that carry the directions
- Totals the kinetic energy before and after and classifies the collision from the comparison
- Says where the missing kinetic energy has gone in an inelastic collision
1 · Read
Momentum is mass times velocity, and it carries direction. Pick one direction as positive and keep it for every object, before and after. When outside forces are tiny during the brief smash, total momentum before equals total momentum after. Inside forces cancel in pairs and never change the total.
An elastic hit keeps all its kinetic energy. The pair deform and spring back with nothing lost to heat, sound, or dents. To sort a real crash, total the kinetic energy before and after. Equal totals mean elastic, and a smaller total after means inelastic.
In the extreme case the pair stick together and share one final velocity. The lost energy has not vanished. It heated metal, made sound, and bent shapes for good. The gap between the totals is the receipt for the crash.
Balance momentum with signs, audit the kinetic energy, and name the crash from the gap.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.