---
title: momentOfInertia
framework: scenekit
role: symbol
role_heading: Instance Property
path: scenekit/scnphysicsbody/momentofinertia
---

# momentOfInertia

The body’s moment of inertia, expressed in the local coordinate system of the node that contains the body.

## Declaration

```swift
var momentOfInertia: SCNVector3 { get set }
```

## Discussion

Discussion A body’s moment of inertia determines how it responds to torques (that is, forces with a rotational component). Each component of this vector is the moment of inertia for the corresponding principal axis (in the coordinate system containing the physics body). For example, if the x-component value of the moment vector is less than the y-component value, the body rotates more freely about its x-axis than its y-axis. By default, SceneKit automatically determines the body’s moment of inertia based on its shape and mass. Use this property to define a custom moment of inertia (for example, to model an object of non-uniform density). Using a custom moment of inertia requires setting the usesDefaultMomentOfInertia property to false.

## See Also

### Defining a Body’s Physical Properties

- [mass](scenekit/scnphysicsbody/mass.md)
- [charge](scenekit/scnphysicsbody/charge.md)
- [friction](scenekit/scnphysicsbody/friction.md)
- [rollingFriction](scenekit/scnphysicsbody/rollingfriction.md)
- [restitution](scenekit/scnphysicsbody/restitution.md)
- [damping](scenekit/scnphysicsbody/damping.md)
- [angularDamping](scenekit/scnphysicsbody/angulardamping.md)
- [usesDefaultMomentOfInertia](scenekit/scnphysicsbody/usesdefaultmomentofinertia.md)
- [centerOfMassOffset](scenekit/scnphysicsbody/centerofmassoffset.md)