How do I make a rigidbody move on command (ie A Player Character)?

This code works but only when the rigidbody's in the air.

 #pragma strict
 
 var MovementSpeed : float;
 var JumpHeight : float;
 private var MovementVer : int;
 private var MovementHor : int;
 
 function Update() {
 
     MovementVer = Input.GetAxis("Vertical") * MovementSpeed * Time.deltaTime;
     MovementHor = Input.GetAxis("Horizontal") * MovementSpeed * Time.deltaTime;
     
     rigidbody.AddForce(MovementHor, 0, MovementVer);
     
 
     }