Doing something onCollisionEnter

Hey guys, im trying to add force to objects inside the sphere but im getting errors, Help would be much appreciated.

Assets/Scripts/gravityfmk.cs(18,14): error CS0111: A member `gravityfmk.OnCollisionEnter(UnityEngine.Collision)’ is already defined. Rename this member or use different parameter types

using UnityEngine;
using System.Collections;

public class gravityfmk : MonoBehaviour
{

	public float gforce= 5;
	public Vector3 z3 = new Vector3( 0, 0, 1);

	void OnCollisionEnter (Collision gravity)
	{
		if(gravity.gameObject.name == "Asteroid-001-LowPoly")
		{
			GetComponent<Rigidbody>().AddForce (z3 * gforce);
		}
	}

	void OnCollisionEnter (Collision gravity2)
	{
		if(gravity2.gameObject.name == "Asteroid-002-LowPoly")
		{
			GetComponent<Rigidbody>().AddForce (z3 * gforce);
		}
	}
}

You can only declare one OnCollisionEnter

Instead of writing two of them, just do:

 void OnCollisionEnter (Collision gravity)
 {
     if(gravity.gameObject.name == "Asteroid-001-LowPoly" || gravity.gameObject.name == "Asteroid-002-LowPoly")
     {
         GetComponent<Rigidbody>().AddForce (z3 * gforce);
     }
 }