How to enable gravity when touched.

Okay, I am a very very bad at code. And I need help with this script. I need my game object to fall to the ground when tapped on an iOS devise. I have a script I put together already, but it doesn’t work. Here is the script: `using UnityEngine;
using UnityEngine;
using System.Collections;

using UnityEngine;
using System.Collections;

public class GravityEnable : MonoBehaviour {
private Rigidbody rigidbody;

void Start ()
{
	  GetComponent<Rigidbody>();
}
// Update is called once per frame
void Update () {  if (Input.touchCount == 1) {
		rigidbody.useGravity = true;
		

	}
}

}

So, this what I have now. Can anyone help?

Can you describe exactly what you are trying to do? Can you be specific about the behaviour you are trying to create, as compared to what is actually happening?

For example, you said you tested the object and all objects fall when touched, which is what you said you wanted. What is it that you want to be different?