Why wont my character stop moving when it collides with the obstacles?,Why doesn't my movement script stop?

So basically I am making a game, I am a beginner watching Brackey's tutorials (see https://www.youtube.com/watch?v=gAB64vfbrhI) and it the code gives me errors and I would like help. He is the script [code=CSharp]using UnityEngine;

public class PlayerCollison : MonoBehaviour {

 public PlayerMovement movement;

 void OnCollisionEnter(Collision collisionInfo)
 {
     if (collisionInfo.collider.tag == "Obstacle")
     {
         movement.enabled = false;

} } }[/code] Here is the Movement Script [code=CSharp]using UnityEngine;

public class PlayerMovement : MonoBehaviour { // "RB" Refrences RigidBody public Rigidbody rb;

 // Variable for players foward movement
 public float fowardForce = 2000f;
 public float sidewaysForce = 500f;

 // "FixedUpdate" is for physics
 void FixedUpdate()
 {
     // Gives the player their foward movement
     // Variable "fowardForce" has a defualt value of 2000
     rb.AddForce(0, 0, fowardForce * Time.deltaTime);

     if ( Input.GetKey("d") )
     {
         rb.AddForce(sidewaysForce * Time.deltaTime, 0, 0);

     }
     if (Input.GetKey("a"))
     {
         rb.AddForce(-sidewaysForce * Time.deltaTime, 0, 0);

     }
 }

}[/code] Here is a video of what happens link text

[1]: https://www.youtube.com/watch?v=gAB64vfbrhI