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# usesDefaultMomentOfInertia

A Boolean value that determines whether SceneKit automatically calculates the body’s moment of inertia or allows setting a custom value.

```
var usesDefaultMomentOfInertia: Bool { get set }
```

## Discussion

A body’s moment of inertia determines how it responds to torques (that is, forces with a rotational component).

If this property is <doc://com.apple.documentation/documentation/Swift/true> (the default), SceneKit automatically determines the body’s moment of inertia based on its shape and mass. Set this property to <doc://com.apple.documentation/documentation/Swift/false> and use the [`momentOfInertia`](/documentation/SceneKit/SCNPhysicsBody/momentOfInertia) property to define a custom moment of inertia (for example, to model an object of non-uniform density).

---

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