Why does my 2D box tip over for no reason?

Center of Mass is offset from the geometric center. Either Use Auto Mass derives a wonky value from the collider shape, or you set centerOfMass explicitly to a bad point. Set centerOfMass = Vector2.zero (or where physics expects) and confirm with the gizmo.

What is Use Auto Mass?

Rigidbody2D computes mass from collider area * density. Useful but can yield surprising centerOfMass for compound colliders. Disable for hand-tuned mass.

Should I weight the bottom for stability?

Yes for tall objects (lampposts, characters). centerOfMass = Vector2(0, -collider_height * 0.4) puts mass low; tipping requires more torque.

Fix: Unity Rigidbody2D Center of Mass Tipping

Quick answer: Set Rigidbody2D.centerOfMass explicitly. For tall props, lower the center to (0, -h*0.4). Disable Use Auto Mass when manually tuning. Verify with Physics 2D gizmos.

A barrel sits stable, then suddenly tips. Compound collider shifted the auto-computed center of mass to one side; gravity acts off-axis.

The Symptom

Static physics object tips or rolls unexpectedly. Disabling Use Auto Mass and setting mass manually fixes it — or makes it worse if you didn’t reset centerOfMass.

The Fix

var rb = GetComponent<Rigidbody2D>();
rb.useAutoMass = false;
rb.mass = 10f;
rb.centerOfMass = new Vector2(0, -0.4f);   // for a 1m tall prop, mass low

Lower CoM = harder to tip. Higher CoM = topples easily. Tune to the design.

Visualizing

Window → Analysis → Physics Debugger → show centerOfMass. A red dot. Confirms where mass is “balanced.”

Compound Colliders

Multiple Collider2Ds add up. Auto mass computes weighted average; manually overriding centerOfMass overrides the auto choice.

Verifying

Drop the object. Should sit stable. Push lightly; tips proportionally to CoM height. Without override: random tipping.

“CoM low for stability. Override Auto. Visualize to confirm.”

Related Issues

For static-vs-static collision callbacks, see collision callbacks. For Rigidbody sleep, see sleep waking.

Mass low. Tipping resists.