Advanced Features

Physics Constraints and Inertial Motion

Add physics to a target bone and understand inertia, strength, damping, mass, gravity, and wind.

AdvancedAbout 24 minFor Editor v1.0 · Tutorial updated Oct 26, 2026

After this article

Create controlled inertial motion and tune it in small steps without losing stability.

1
Select a target bone or continuous chain
Choose a bone that should follow with inertia. For the exercise, avoid a part that is essential to the character's stable stance; a bone cannot have duplicate physics constraints.
2
Add a physics constraint
Use Physics Constraint in Add Relation or the PHY canvas tool. With a continuous selection, the editor creates constraints for eligible bones.
Expected resultThe inspector shows the target bone and physics parameters, with simulation enabled by default.
Physics belongs to the target bone; verify the target before tuning.
3
Create a comparison
Play a default animation before increasing the physics influence. Disable simulation for comparison when needed, but never change several parameters at once.
Expected resultYou can distinguish the original keyframed motion from the added physics.

Parameter	What it feels like	How to approach it
Mix	How strongly physics affects the final pose	Start with a small influence rather than overriding the keys
Inertia	The follow-through response to changes in motion	Observe before adjusting; too much can delay and overshoot
Strength	The force returning toward the target state	Tune together with damping rather than maximizing alone
Damping	How quickly oscillation decays	Increase moderately if swaying continues too long
Mass	The heaviness of the motion response	Changes overall response, not the image's visual weight
Gravity / wind	Continuous external influence	Confirm the coordinate direction and add a small amount
Limit	Allowed motion range	Prevents abnormal overshoot but does not replace sensible tuning

1
Refine with numeric fields
Sliders commit on release; numeric fields commit on Enter or blur. Play the same animation segment after every change.
Expected resultMotion settles without persistent jitter or sudden folding.
Change one parameter at a time and compare the same segment.
2
Inspect translate, rotate, shear, and scale channels
Enable only the channels needed for the intended effect and keep unrelated channels at zero.
Expected resultPhysics affects only the planned motion dimensions.

Check stability in idle and follow-through and damping in walk / run.
Inspect the target bone's images, children, and other constraints for conflicts with manual keys.
Check for unwanted continued motion at loop endpoints and the death final pose.
Verify by reimporting or using the target Spine runtime. Different versions can express physics and IK differently, so editor preview alone is insufficient.