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# acceleration

The constant acceleration vector, in units per second per second, applied to all particles in the system. Animatable.

```
var acceleration: SCNVector3 { get set }
```

## Discussion

Use this property to simulate effects such as wind or gravity on particles.

To use the same gravity vector that applies to physics bodies in the scene, or to apply more than one constant acceleration to particles, see the [`isAffectedByGravity`](/documentation/SceneKit/SCNParticleSystem/isAffectedByGravity) property.

The default value is [`SCNVector3Zero`](/documentation/SceneKit/SCNVector3Zero), specifying no acceleration.

You can animate changes to this property’s value. See [Animating SceneKit Content](/documentation/SceneKit/animating-scenekit-content).

---

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