Jumping Script not working

I am using javascript to make sure that my player is grounded before it lets it drop. It gives me and error, it doesn’t seem to like the fact that I’m referring rigidbody.

Code:

#pragma strict
private var IsGrounded = false;

 function OnCollisionStay ()
 {
     IsGrounded = true;    
 }
 function OnCollisionExit ()
 {
     IsGrounded = false;    
 }
 
 if (IsGrounded == false)
 {
	 if(Input.GetKey(KeyCode.Space))
	 {
		 Rigidbody.AddForce (0, 50, 0);
	 }
 }

Error:
BCE0020: An instance of type ‘UnityEngine.Rigidbody’ is required to access non static member ‘AddForce’.

You need an instance of RigidBody component, this is how you can get it:

GetComponent.<Rigidbody>().AddForce(0, 50, 0);