Riigidbody.MovePosition automaticly starts spinning.

I have just started learning how to use unity, and I would like to make smooth controls with ridigbodys. I have used the AddForce function, but I couldn't get that to stop moving after it started, so I researched a little bit and found the MovePosition function, but the thing is, it just starts automatically spinning. I would like to know how to use this function properly. Also this is my first time posting on this forum and please tell me if I should have posted this in the programming section. Thank you all very much.

Here's my code:

Code (CSharp):

1. using UnityEngine;
2.  
3. public class playerController : MonoBehaviour {
4.     // I define this in the Inspector tab
5.     public Rigidbody rb;
6.  
7.     void FixedUpdate() {
8.         if (Input.GetKey("w")) {
9.             Vector3 move = new Vector3(0, 0, 1) * forwardForce *Time.deltaTime;
10.             rb.MovePosition(move);
11.             Debug.Log("Moved using w key");
12.  
13.         }
14.     }
15. }