home / skills / dylantarre / animation-principles / physics-intuition
This skill helps you imbue animation with believable physics by applying mass, timing, and momentum principles to motion and weight.
npx playbooks add skill dylantarre/animation-principles --skill physics-intuitionReview the files below or copy the command above to add this skill to your agents.
---
name: physics-intuition
description: Use when motion needs to feel physically grounded—objects falling, characters jumping, things colliding, or any element that should obey believable weight and momentum.
---
# 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.
This skill teaches how to make motion read as believable weight and momentum in animation. It translates physics principles into practical animation choices so objects and characters feel convincingly heavy, light, or elastic. Use it to ground motion in cause-and-effect while preserving expressive intent.
It frames animation decisions around a simple mental model: ask what something weighs and how that mass affects timing, arcs, and secondary motion. The skill maps each of the key animation principles to physical behaviors—squash & stretch for volume conservation, slow in/slow out for acceleration, arcs for gravity-driven paths, and so on. It then gives concrete fixes for common problems like floatiness, stiffness, or unrealistic stops.
When should I break real physics for believability?
Break physics when the emotional or readable result improves—common in anticipation, hang-time, and exaggerated squash—so long as the inconsistency serves the story and is applied consistently.
How do I decide perceived mass quickly?
Compare to familiar references (feather vs. bowling ball). If an audience should 'feel' effort or resistance, treat it as heavier: slower starts/stops, stronger ease curves, and more pronounced settling.