Physics engine / 2026-03-25 / Harsha
Simple dynamics
This lerpette starts with two of the smallest useful ideas in rigid body simulation: a force accumulating over time, and an impulse changing velocity immediately.
01
Accumulated force
Forces act over time, so they usually change velocity through integration.
The point of this chapter is just to separate “push over time” from “instant change.” Once that distinction is clear, the rest of the engine starts to organize itself.
02
Impulse as an immediate correction
Impulses are useful when the change is instantaneous.
That is why impulses show up naturally in collisions and constraints: they correct the velocity state directly instead of being accumulated like forces.
velocity += impulse / mass;
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