How real is the physics engine?

Unity Engine
1

I was thinking of using unity3d to demonstrate some basic physics, but I wonder how accurate the simulation is. As a first small test I just used two spheres that has the same Y and Z positions and different X positions. I add a velocity on the X axis on ball A and make it move towards ball B.

Since they have the same size and mass I would expect the momentum of ball A to be completely transfered to ball B (like shooting a pool ball cleanly on another), but after the collision both balls are moving in more or less the same speed.

Am I doing something wrong, or isn’t Unity good for simulating these kind of physics demos?

2

You have to keep in mind that the physics engine has to run in realtime and therefore it won’t be 100% accurate.
Try to lower the “Fixed Timestep”, which will increase the accuracy and probably make it accurate enough for your purposes. Check out Unity - Manual: Time

3

With a little more playing with physics materials I got the expected behaviour by setting the friction to 0 and the bounciness to 1. Now I just need to read more to understand why.