Elastic Collision Calculator
Works out what happens after a perfectly bouncy collision.
After the collision
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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Mass 1 velocity after —
Mass 2 velocity after —
Total momentum — kg·m/s
Total kinetic energy —
Assumes —
The formula
v₁ = ((m₁ − m₂)u₁ + 2m₂u₂) ÷ (m₁ + m₂) v₂ = ((m₂ − m₁)u₂ + 2m₁u₁) ÷ (m₁ + m₂)
Both momentum and kinetic energy are conserved, which fixes both final velocities.
What to watch out for
Enter one velocity as negative if the objects approach from opposite directions.
Frequently Asked Questions
What happens when equal masses collide elastically?
They swap velocities. Two 1 kg masses at 3 m/s and 0 m/s finish at 0 and 3 m/s.
What about a light ball hitting a heavy wall?
It bounces back at almost the same speed. A 1 kg ball at 3 m/s hitting a still 1,000 kg mass leaves at -2.994 m/s.