Elastic and Inelastic Collisions in 2D

What you are seeing: two disks of mass $m_1, m_2$ collide obliquely with an adjustable impact parameter $b$ and coefficient of restitution $e$ . The collision is resolved along the contact normal: that component reverses scaled by $e$ , the tangential component is unchanged. Momentum is conserved componentwise for any $e$ ; kinetic energy only for $e = 1$ . Head-on ( $b = 0$ ) is the familiar 1D case.

Figure 1. Two-disk 2D oblique collision with adjustable restitution and impact parameter; componentwise momentum conserved, kinetic energy lost for e < 1.

m11.0

m22.0

speed v13.0

impact b0.40

e (restitution)0.60

WHAT TO TRY

Set $e = 1$ for a perfect bounce: the kinetic-energy line stays flat. Lower $e$ and watch energy drop at the moment of impact while momentum does not.
Slide the impact parameter $b$ from a head-on hit to a glancing graze and watch the scatter angle open up.
Change the masses: the total-momentum arrow in the corner never changes length, however the two disks share it out.