Collisions in Two Dimensions
Conserve momentum separately in x and y.
About this topic
In a 2D collision, momentum is conserved separately along the x and y axes. Resolve each velocity into components, write one equation per direction, and solve. If the collision is elastic, kinetic energy gives an additional equation.
Equal-mass elastic collisions with a stationary target make the two objects leave at 90 degrees to each other, as seen in billiards and in collisions between particles in physics experiments. The total momentum vector before equals the total after, so the sum of the final momentum vectors must match the starting one.
Example: a 0.2 kg ball moving at 5 m/s east strikes a stationary identical ball. If the first ball goes off at 30 degrees north of east at 4.33 m/s, the second travels at 2.5 m/s at 60 degrees south of east, satisfying both momentum components and the energy. Car crashes at intersections are analysed this way by investigators to find speeds.
Tips: sketch before and after, choose axes along the incoming direction, and handle each component separately. Common errors include adding magnitudes of momentum instead of components, and applying kinetic energy conservation to an inelastic collision.
Key ideas
- Break momenta into components
- Write equations for x and y
- Billiard balls scatter at right angles
Quick check
Use cases: where Collisions in Two Dimensions helps
- Homework: review the key idea behind Collisions in Two Dimensions before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Collisions in Two Dimensions without notes.
- Visual learning: play with the interactive lab to see how Collisions in Two Dimensions changes when you adjust its inputs.
- Teaching a friend: explain Collisions in Two Dimensions 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 Collisions in Two Dimensions?
Conserve momentum separately in x and y.
What will I learn in Collisions in Two Dimensions?
Break momenta into components. Write equations for x and y. Billiard balls scatter at right angles.
Is Collisions in Two Dimensions 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 Collisions in Two Dimensions 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 Collisions in Two Dimensions?
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.