# OnCollisionEnter(Collision)

> OnCollisionEnter is called when this collider/rigidbody has begun touching another rigidbody/collider.

## Definition

* **Type:** Method
* **Namespace:** [UnityEngine](/engine/6000.3/script-reference/unityengine.md)

## OnCollisionEnter()

```csharp
public void OnCollisionEnter(Collision collision)
```

### Parameters

**** (\[Collision]\(/engine/6000.3/script-reference/unityengine/collision)): 

### Remarks

`OnCollisionEnter` receives an instance of the [Collision](/engine/6000.3/script-reference/unityengine/collision.md) class as the `collision` parameter. This parameter contains information about the collision such as contact points and impact velocity. If you don't use this collision data in your `OnCollisionEnter` callback, leave out the `collision` parameter from the method declaration to avoid unneccessary calculations. **Note:** Collision events are only sent if one of the colliders also has a non-kinematic rigidbody attached. Collision events will be sent to disabled MonoBehaviours, to allow enabling Behaviours in response to collisions. `OnCollisionEnter` can be a [coroutine](/engine/6000.3/manual/scripting/object-oriented-development/coroutines-section/coroutines.md)

### Examples

```csharp

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    AudioSource audioSource;

    void Start()
    {
        audioSource = GetComponent<AudioSource>();
    }

    void OnCollisionEnter(Collision collision)
    {
        foreach (ContactPoint contact in collision.contacts)
        {
            Debug.DrawRay(contact.point, contact.normal, Color.white);
        }

        if (collision.relativeVelocity.magnitude > 2)
            audioSource.Play();
    }
}
```