Collision.contacts

Description

The contact points generated by the physics engine. You should avoid using this as it produces memory garbage. Use GetContact or GetContacts instead.

Every contact contains a contact point, normal and the two colliders that collided (see ContactPoint). From inside OnCollisionStay or OnCollisionEnter you can always be sure that contacts has at least one element.

using UnityEngine;

public class ExampleScript : MonoBehaviour
{
    void OnCollisionStay(Collision collision)
    {
        foreach (ContactPoint contact in collision.contacts)
        {
            print(contact.thisCollider.name + " hit " + contact.otherCollider.name);
            // Visualize the contact point
            Debug.DrawRay(contact.point, contact.normal, Color.white);
        }
    }
}

// A grenade
// - instantiates a explosion Prefab when hitting a surface
// - then destroys itself

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    public Transform explosionPrefab;
    void OnCollisionEnter(Collision collision)
    {
        ContactPoint contact = collision.contacts[0];
        Quaternion rot = Quaternion.FromToRotation(Vector3.up, contact.normal);
        Vector3 pos = contact.point;
        Instantiate(explosionPrefab, pos, rot);
        Destroy(gameObject);
    }
}