Which of the following physical laws can make a simulated collision seem more realistic?

Motion

Gravity

Fluid dynamics

Thermodynamics

Short answer: Motion

Long answer: It depends on the type of simulation is being run, if it's between large masses such as planets, gravity is a must-have, for differing temperatures, thermodynamics, for liquids, liquid Dynamics, but most have one thing in common, they all do not seem realistic without motion.