# rotationBySpeed

> Script interface for the RotationBySpeedModule of a Particle System.

## Definition

* **Type:** Property
* **Namespace:** [UnityEngine](/engine/6000.7/script-reference/unityengine.md)
* **Assembly:** UnityEngine.ParticleSystemModule

```csharp
public ParticleSystem.RotationBySpeedModule rotationBySpeed { get; }
```

### Remarks

Rotate particles based on their speed.

Particle System modules do not need to be reassigned back to the system; they are interfaces and not independent objects.

### Examples

```csharp
using UnityEngine;
using System.Collections;

[RequireComponent(typeof(ParticleSystem))]
public class ExampleClass : MonoBehaviour {
    void Start() {
        ParticleSystem ps = GetComponent<ParticleSystem>();
        var rot = ps.rotationBySpeed;
        rot.enabled = true;

        AnimationCurve curve = new AnimationCurve();
        curve.AddKey(0.0f, 0.1f);
        curve.AddKey(0.75f, 0.6f);

        AnimationCurve curve2 = new AnimationCurve();
        curve2.AddKey(0.0f, 0.2f);
        curve2.AddKey(0.5f, 0.9f);

        rot.z = new ParticleSystem.MinMaxCurve(2.0f, curve, curve2);
    }
}
```