---
title: SCNParticleModifierStage.preDynamics
framework: scenekit
role: symbol
role_heading: Case
path: scenekit/scnparticlemodifierstage/predynamics
---

# SCNParticleModifierStage.preDynamics

The stage before SceneKit simulates the motion of particles.

## Declaration

```swift
case preDynamics
```

## Discussion

Discussion Insert a modifier block at this stage to alter the inputs to the dynamics simulation. For example, if you modify the velocities of particles during this stage, SceneKit computes new positions for each particle based on its modified velocity.

## See Also

### Constants

- [SCNParticleModifierStage.postDynamics](scenekit/scnparticlemodifierstage/postdynamics.md)
- [SCNParticleModifierStage.preCollision](scenekit/scnparticlemodifierstage/precollision.md)
- [SCNParticleModifierStage.postCollision](scenekit/scnparticlemodifierstage/postcollision.md)