An instance of type 'UnityEngine.Rigidbody' is required to access non static member 'AddRelativeTorque'. - I don't understand the problem

[1]Hello, I need help with this script because i don’t understand the problem

#pragma strict

var rotationSpeed = 100;

function Update () 
	var rotation : float = Input.GetAxis ("Horizontal") * rotationSpeed;
	rotation *= Time.deltaTime;
	UnityEngine.Rigidbody.AddRelativeTorque (Vector3.back * rotation);


rigidbody.AddRelativeTorque (Vector3.back * rotation);

It is rigidbody with a small ‘r’

I think should be… GetComponent.().AddRelativeTorque(Vector3.back * rotation);