skills/material3-expressive-flutter/rules/motion-physics.md

Motion Physics Rule

All M3 Expressive animations must use physics-based springs instead of fixed durations/easing where possible.

Spatial Springs

Use for movement, position, and layout changes.

• Goal: Mirror real-world object physics.
• Flutter Implementation: Curves.elasticOut, Curves.bounceOut, or SpringSimulation.
• Primary Curve: Cubic(0.34, 1.56, 0.64, 1) (The Expressive Curve).

Effects Springs

Use for non-spatial properties like color, opacity, and scale.

• Goal: Smooth, responsive transitions.
• Flutter Implementation: Curves.easeInOutCubic or Curves.fastOutSlowIn.

Standards

1. Interactive Feedback: All touch interactions must trigger a scale or translation response using a Spatial spring.
2. Speed: Response must be immediate (<50ms start) even if the settling takes longer.
3. Co-ordination: Co-ordinate visual motion with HapticFeedback.lightImpact().