Bezier curves are a lie.
Bezier easing curves borrow the visual grammar of physical motion without its underlying logic. When a real object moves, it responds to forces: inertia, friction, elasticity. Bezier curves approximate the result without capturing the cause.
Enter spring physics.
Spring-based systems replace curves with physics parameters: mass, stiffness, and damping. Spring physics are interruptible — when interrupted mid-flight, they respond naturally rather than snapping to a new state. This is what makes interfaces feel alive.
Tuning your springs.
High stiffness means fast, snappy motion — good for micro-interactions. Low stiffness means slow, loping motion — better for layout transitions. Damping controls overshoot. Mass affects the overall feel of weight.
When not to use springs.
For purely choreographed animation — a loading sequence, a cinematic transition — Bezier curves remain the right tool. The question: does this animation respond to input, or does it play out on its own?
The meta-lesson.
Both tools are just ways of asking: what does this element weigh, and how does it want to move? When you can answer that intuitively, the technical implementation becomes secondary.