Elastic and Inelastic Collisions
Elastic collisions conserve kinetic energy; inelastic ones don't.
About this topic
In an elastic collision both momentum and kinetic energy are conserved, as for billiard balls or gas molecules (approximately). In an inelastic collision momentum is conserved but some kinetic energy turns into heat, sound or deformation. If the objects stick together it is perfectly inelastic, losing the most energy allowed.
In real life, collisions fall between the extremes. The coefficient of restitution measures bounciness, being the ratio of separation speed to approach speed, equal to 1 for elastic and 0 for perfectly inelastic. In a one-dimensional elastic collision between equal masses, the objects swap velocities.
Example: a 1 kg ball at 4 m/s hits an identical stationary ball elastically, stopping dead while the second leaves at 4 m/s, as in Newton's cradle. In a car crash, the metal crumples and kinetic energy goes into deformation, which is inelastic but useful because it absorbs the energy.
Misconception: momentum is conserved in all collisions without external forces, but kinetic energy is conserved only in elastic ones. Do not use the energy equation for an inelastic collision.
Key ideas
- Momentum is conserved in both
- Perfectly inelastic: objects stick
- Real collisions lose some KE
Quick check
Use cases: where Elastic and Inelastic Collisions helps
- Homework: review the key idea behind Elastic and Inelastic Collisions before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Elastic and Inelastic Collisions without notes.
- Visual learning: play with the interactive lab to see how Elastic and Inelastic Collisions changes when you adjust its inputs.
- Teaching a friend: explain Elastic and Inelastic Collisions in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Elastic and Inelastic Collisions?
Elastic collisions conserve kinetic energy; inelastic ones don't.
What will I learn in Elastic and Inelastic Collisions?
Momentum is conserved in both. Perfectly inelastic: objects stick. Real collisions lose some KE.
Is Elastic and Inelastic Collisions part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Elastic and Inelastic Collisions lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Elastic and Inelastic Collisions?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.