Question 1

Why do pool balls separate at 90° after a collision?

Accepted Answer

When two equal-mass balls collide and one is stationary, momentum conservation requires their final velocities to be perpendicular — they fly off at exactly 90° to each other. This is because kinetic energy conservation plus momentum conservation constrains the angle to 90° in the equal-mass case.

Question 2

What is an elastic collision?

Accepted Answer

An elastic collision conserves both momentum AND kinetic energy. Pool balls approximate this well because they are hard and don't deform much. In a perfectly elastic head-on collision between equal masses, the first ball stops completely and the second takes all its speed.

Question 3

How does rolling friction work on a pool table?

Accepted Answer

The felt surface creates friction that decelerates the ball. In this simulator, each frame the horizontal velocity is multiplied by a friction coefficient (0.995 for felt). This gradually slows the ball until it stops — just like a real table.

Question 4

How do cushion bounces work?

Accepted Answer

When a ball hits a cushion (wall), the velocity component perpendicular to the wall is reversed with some energy loss (restitution ~0.85). The parallel component continues unchanged. This is why you can bank shots off the rails at predictable angles.

Question 5

Why is this a good way to learn physics?

Accepted Answer

Billiards is one of the purest examples of Newtonian mechanics. Every shot demonstrates momentum conservation, energy transfer, friction, and reflection. The 3D simulator lets you see these principles in action and experiment with different shots.

Billiards Physics