# externalForces

> Script interface for the ExternalForcesModule of a Particle System.

## Definition

* **Type:** Property
* **Namespace:** [UnityEngine](/engine/6000.0/script-reference/unityengine.md)
* **Assembly:** UnityEngine.ParticleSystemModule

```csharp
public ParticleSystem.ExternalForcesModule externalForces { get; }
```

### Remarks

This module enables [ParticleSystemForceField](/engine/6000.0/script-reference/unityengine/particlesystemforcefield.md) and [WindZone](/engine/6000.0/script-reference/unityengine/windzone.md) components to affect the Particle System.

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 ex = ps.externalForces;
        ex.enabled = true;
        ex.multiplier = 0.1f;
    }
}
```