dylantarre/animation-principles/physics-intuition

Physics Intuition

Think like a physicist watching the world move. Every object has mass. Every motion has cause and consequence.

Core Mental Model

Before animating anything, ask: What does this weigh?

A feather and a bowling ball both fall, but they tell completely different stories. Your job is to make the audience feel that weight without thinking about it.

The 12 Principles Through Physics

Squash & Stretch — Mass is conserved. When something compresses, it must bulge. A bouncing ball flattens on impact because its volume has to go somewhere.

Timing — Heavy = slow to start, slow to stop. Light = quick reactions. A truck and a bicycle brake very differently.

Slow In & Slow Out — Nothing starts or stops instantly. Acceleration and deceleration are the fingerprints of mass.

Arcs — Gravity curves everything. Even a punch follows a pendulum path from the shoulder. Straight lines feel robotic.

Secondary Action — When the main mass moves, attached masses follow with delay. Hair, clothing, jowls—they're all passengers on the physics train.

Follow Through & Overlapping Action — Different masses have different momentum. A character stops, but their belly keeps going. This is inertia made visible.

Anticipation — Force requires windup. You can't push without first pulling back. Show the gathering of energy before release.

Exaggeration — Push physics past reality to feel more real. A heavy landing needs more squash than actual physics would produce.

Staging — Position elements so physical relationships read clearly. The audience must understand spatial cause and effect.

Straight Ahead & Pose to Pose — Use straight ahead for chaotic physics (explosions, water). Use pose to pose for controlled physics (a character lifting something).

Solid Drawing — Volume must remain consistent. A character can't lose mass between frames without the audience noticing something is wrong.

Appeal — Even physics follows design. Decide if your world has cartoon physics or realistic physics, then be consistent.

Practical Application

When something feels "floaty" or "weightless":

1. Add more ease-in at the start of motion
2. Increase ease-out at stops
3. Add settling oscillations (things don't stop perfectly still)
4. Check that secondary elements lag appropriately

When something feels "stiff":

1. Introduce squash at impact points
2. Add stretch during fast movement
3. Ensure arcs in all trajectories
4. Let different body parts arrive at different times

The Golden Rule

Audiences don't analyze physics—they feel it. Your job isn't accuracy; it's believability. Sometimes breaking physics (hanging in mid-air before a fall) creates more convincing weight than obeying it.