Rocks that fall on collision

Questions & Answers
1

I was wondering how to make a script that says when something collides with it will fall and just floats in mid air when nothing collides with it. This is my script:

using UnityEngine;
using System.Collections;

public class Rock : MonoBehaviour {

	// Use this for initialization
    void Start()
    {
        Physics2D.gravity = new Vector2(0, 0);
    }
	
	// Update is called once per frame
    void OnTriggerEnter2D(Collider2D col)
    {
        if (col.CompareTag("Player"))
        {
            Physics2D.gravity = new Vector2(0, -1);
        }

    }
     void OnTriggerExit2D(Collider2D col)
    {
        if (col.CompareTag("Player"))
        {
            Physics2D.gravity = new Vector2(0, -1);
        }

    }
}

Any help?

2

How about adding a RigidBody on runtime with a collision event? This way the Unity physics engine will handle it.