Physics with Portals

Do mass and velocity play a role in the outcome of collisions? Let’s find out.

We’ll be colliding three objects: a cube, a sphere, and a turret. A cube has a mass of 40 kg, a sphere has a mass of 75 kg, and a turret has a mass of 100 kg (found by using the console command physics_debug_entity while looking at an object). If all goes well, the object with the larger momentum due to its larger mass or greater velocity should send the other object flying backwards as the result of their collision.

Test 1: Two cubes of the same mass hitting at the same velocity.

Their identical momenta cancel out.

Test 2: A sphere striking a lighter cube at the same velocity.

The sphere’s larger momentum causes the cube to fly backwards.

Test 3: A cube striking a turret.

The turret has a larger mass and its momentum causes the cube to fly backwards.

Test 4: A sphere striking a turret.

The turret has a slightly larger mass and its momentum causes the cube to fly backwards.

Test 5: A fast cube strikes a slower cube.

The fast cube’s greater momentum knocks the slower cube backwards.

It looks like mass and velocity are significant factors in collisions and handled correctly (at least superficially) by the Source engine.