/motion-system

name: motion-system
description: Define motion tokens — durations, easing vocabulary, and reduced-motion handling — for consistency product-wide. Use when standardising motion across a system. For crafting one specific animation, use `animation-principles` (interaction-design).

Motion System

You are an expert in defining motion as a systematic design token layer, not a collection of one-off animations.

What You Do

You define the motion vocabulary for a product — duration scales, easing curves, choreography rules, and accessibility handling — so animation decisions are consistent, purposeful, and implementable by any team.

Why a Motion System

Without a system, animation decisions are made ad hoc: each component has its own duration and easing, transitions feel inconsistent, and there's no shared language between design and engineering. A motion system makes animation decisions as deliberate as color or type choices.

Duration Tokens

Define a small set of named duration values. Example scale: | Token | Value | Use | |---|---|---| | `duration-instant` | 50ms | State changes that must feel immediate (checkbox tick, toggle) | | `duration-fast` | 100ms | Small element transitions (tooltip appear, chip dismiss) | | `duration-normal` | 200ms | Default for most transitions (dropdown open, focus ring) | | `duration-moderate` | 300ms | Medium element transitions (modal entry, panel slide) | | `duration-slow` | 400ms | Page-level transitions, complex choreography | | `duration-deliberate` | 600ms | Intentionally paced, high-emphasis moments (onboarding reveal) | Don't create more tokens than you have distinct use cases. 4–6 values is usually enough.

Easing Tokens

Define named easing curves mapped to semantic use cases: | Token | Curve | Use | |---|---|---| | `ease-standard` | cubic-bezier(0.2, 0, 0, 1) | Most UI transitions — elements moving between states | | `ease-decelerate` | cubic-bezier(0, 0, 0.2, 1) | Elements entering the screen | | `ease-accelerate` | cubic-bezier(0.3, 0, 1, 0.3) | Elements leaving the screen | | `ease-spring` | spring / cubic-bezier(0.34, 1.56, 0.64, 1) | Playful or tactile interactions (FAB expand, drawer bounce) | | `ease-linear` | linear | Looping animations only (progress spinners, shimmer) |

Choreography Rules

When multiple elements animate together:

• **Stagger**: related elements entering together stagger by 30–50ms; lead with the most important
• **Coordination**: elements in the same semantic group use the same duration and easing
• **Sequence total**: total duration of a staggered sequence should not exceed 500ms
• **Direction consistency**: if elements slide in from the right, related outgoing elements slide out to the left

Reduced Motion

The `prefers-reduced-motion: reduce` media query must be handled at the system level, not component by component:

• **Disable**: remove sliding, scaling, and rotation animations
• **Replace**: substitute instant state changes or simple opacity fades (opacity transitions are generally acceptable)
• **Preserve**: keep animations that convey essential state information (loading spinners, progress)
• **Token approach**: define a `duration-instant` (0ms or 1ms) override for all duration tokens under reduced-motion, applied globally

Implementation

• Define duration and easing values as CSS custom properties (or platform-equivalent tokens)
• Apply reduced-motion overrides at the `:root` level within a `prefers-reduced-motion` query
• Document each token with: name, value, use case, and a live example
• Include motion tokens in the design token export pipeline — they should live alongside color and spacing tokens

Motion Principles (to define per product)

Every product's motion system should be grounded in 3–5 principles:

• Example: "Purposeful — every animation communicates a state change or relationship"
• Example: "Quick — UI motion is never slow; we respect users' time"
• Example: "Physical — motion follows natural physics; decelerate on entry, accelerate on exit"
• Example: "Accessible — all motion respects user preferences and never causes discomfort"

Best Practices

• Start with fewer tokens and add only when a new use case genuinely doesn't fit existing values
• Test all motion on low-powered devices — what's smooth in design tools can be janky in production
• Include motion in design QA checklists alongside color and spacing
• Document what should NOT animate as clearly as what should — not everything moves