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# systemSpawnedOnCollision

Another particle system to be added to the scene when a particle collides with scene geometry.

```
var systemSpawnedOnCollision: SCNParticleSystem? { get set }
```

## Discussion

When a particle collides with scene geometry, SceneKit adds a copy of the specified particle system to the scene at the location of the collision. (To define collision behavior, see the [`colliderNodes`](/documentation/SceneKit/SCNParticleSystem/colliderNodes) property.)

Use this property to simulate effects such as rain—one particle system simulates falling raindrops, and another particle system simulates the splashes that occur where each raindrop strikes a surface.

The default value of this property is `nil`, specifying that no additional systems are added to the scene on particle collision.

> Important:
> Adding a new particle system to the scene for each collision can drastically increase the total number of rendered particles. To maintain adequate rendering performance, set the ``doc://com.apple.scenekit/documentation/SceneKit/SCNParticleSystem/loops`` property to <doc://com.apple.documentation/documentation/Swift/false> for any particle system you assign to the ``doc://com.apple.scenekit/documentation/SceneKit/SCNParticleSystem/systemSpawnedOnCollision`` property.

---

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