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# particleVelocity

The initial speed, in units per second, for newly spawned particles. Animatable.

```
var particleVelocity: CGFloat { get set }
```

## Discussion

Particles begin moving at this speed in the direction determined by the [`birthDirection`](/documentation/SceneKit/SCNParticleSystem/birthDirection) or [`emittingDirection`](/documentation/SceneKit/SCNParticleSystem/emittingDirection) property. Their directions and speeds may change thereafter according to the [`acceleration`](/documentation/SceneKit/SCNParticleSystem/acceleration) property or physics effects (see the [`isAffectedByGravity`](/documentation/SceneKit/SCNParticleSystem/isAffectedByGravity), [`isAffectedByPhysicsFields`](/documentation/SceneKit/SCNParticleSystem/isAffectedByPhysicsFields), and [`colliderNodes`](/documentation/SceneKit/SCNParticleSystem/colliderNodes) properties). You can randomize the speed of newly spawned particles with the [`particleAngularVelocityVariation`](/documentation/SceneKit/SCNParticleSystem/particleAngularVelocityVariation) property.

Particle speed is measured in units (of the local coordinate space containing the particle system) per second.

The default value is `0.0` units per second, specifying that newly emitted particles are stationary until otherwise influenced.

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

---

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