Question 1

What is momentum conservation?

Accepted Answer

The total momentum of a closed system (no external forces) never changes. For two objects: m₁v₁ + m₂v₂ = m₁v₁' + m₂v₂'. Momentum is a vector — direction matters. In this simulator, both balls have the same mass and equal-but-opposite velocities, so total momentum is zero before and after.

Question 2

What is the difference between elastic and inelastic collisions?

Accepted Answer

In an elastic collision, both momentum AND kinetic energy are conserved — the balls bounce off at the same speeds they approached (like billiard balls or gas molecules). In an inelastic collision, momentum is still conserved, but kinetic energy decreases — some energy converts to heat, sound, or deformation. Most real collisions are partially inelastic.

Question 3

What is Newton's third law in a collision?

Accepted Answer

During impact, ball 1 exerts a force on ball 2, and ball 2 exerts an equal and opposite force on ball 1. These forces act for the same duration (the contact time), so the impulse (force × time) is equal and opposite — which is why momentum is transferred from one ball to the other.

Question 4

What happens when two equal-mass balls collide head-on in an elastic collision?

Accepted Answer

When two equal-mass balls collide elastically in a head-on collision, they exchange velocities completely. The ball that was moving right stops, and the ball that was moving left stops — they swap speeds exactly. This is the classic result of solving the conservation equations simultaneously.

Question 5

How do I calculate the final velocities after a collision?

Accepted Answer

For an elastic collision between mass m₁ (velocity v₁) and m₂ (velocity v₂): v₁' = (m₁−m₂)v₁/(m₁+m₂) + 2m₂v₂/(m₁+m₂) and v₂' = (m₂−m₁)v₂/(m₁+m₂) + 2m₁v₁/(m₁+m₂). For equal masses, these simplify to v₁' = v₂ and v₂' = v₁ — a perfect velocity swap.

3D Collision Simulator