How to fix jump on Script

I have been tryin to get my rolling ball character to jump for me but I for the life of me cannot get him to do it. The script returns without errors but when I adjust the jump variable nothing changes and the ball wont jump reguardless. Please help! Here is the current script:

using UnityEngine;
using System.Collections;

public class Movement : MonoBehaviour {

public float speed;
public float jumppower;

private Rigidbody rb;

void Start ()
{
	rb = GetComponent<Rigidbody> ();
}

void FixedUpdate ()
{

	float moveHorizontal = Input.GetAxis ("Horizontal");
	float moveVertical = Input.GetAxis ("Vertical");

	Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical); 

	rb.AddForce (movement * speed);

	if (Input.GetButtonDown ("Jump"))
		movement.y = jumppower;

	}

}

Move the

  if (Input.GetButtonDown ("Jump"))
         movement.y = jumppower;
 
     }

so that it’s above rb.AddForce (movement * speed);

You’re assigning the jump power after you’ve already applied your force.