Inertia
Deform shapes from their own motion, as a directional smear or a springy jiggle.
What it does
Inertia adds motion-reactive secondary animation to shapes or geometry. Input motion is measured frame to frame and the shape deforms in reaction, with no hand-keyframed deformation.
Smear stretches the shape backward along its recent trajectory, a directional motion blur baked into the geometry itself. A taper narrows the trailing edge, and volume preservation compresses the cross-section so the stretch does not balloon. Jiggle treats each vertex as a small spring-mass system that overshoots and settles back to rest whenever the object accelerates or stops. Both runs jiggle and smear together.
When to use it
A whip-like streak trailing a fast-moving shape: Smear.
Soft, springy secondary motion (antennae, jelly, cloth-like wobble) reacting to the object's own movement: Jiggle.
A directional streak and a springy settle on the same object: Both.
An object that should hold still when it is still: raise Threshold to ignore tiny jitter at rest.
| Parameter | Type | Default |
|---|---|---|
source | OneOf([Collection]) | — |
inertia_mode | String | "Smear" |
length | Number | 5 |
subdivisions | Number | 8 |
taper | Number | 0.500 |
taper_curve | OneOf([Curve]) | Curve(Easing(BezierSpline { points: [... |
stiffness | Number | 150 |
damping | Number | 12 |
mass | Number | 1 |
substeps | Number | 4 |
threshold | Number | 0.500 |
history_length | Number | 30 |
volume_preservation | Number | 0.500 |
strength | Number | 1 |
Gotchas
Volume Preservation and the taper controls affect Smear only. Jiggle builds no directional streak, so they do nothing in pure Jiggle mode.
Length, how far back the smear stretches, is measured in frames of stored trajectory and is capped by History Length, the maximum trajectory the node keeps. Push Length past History Length and there is not enough history to stretch into, so the streak is clipped short. Raise History Length alongside Length for long streaks.
Threshold is a velocity floor: below it, nothing deforms. Use it to stop Jiggle twitching on sub-pixel motion noise, or to keep Smear from producing a streak while the object is essentially at rest.
Worked example
Add an Inertia node and wire in the shape or geometry to animate.
Set Inertia Mode to Smear, then animate the source's position. Raise Length until the trailing streak reads at your motion speed.
Raise Taper so the tail narrows to a point, and nudge Volume Preservation up so the stretch does not look thin.
Switch Inertia Mode to Both and dial in Stiffness, Damping and Mass so the shape also settles with a springy wobble when it stops.