still got momentum after "Use Gravity" On rigidbody is turned off

I want my player to be able to switch between walking and flying fluently. But after i turn off "Use gravity" on the rigidbody the player has still got the momentum, i was wondering if there is anyway around this? theres probably a easy fix but i just havent seen it yet.

 public float moveSpeed = 15f;

 public float flySpeed = 10f;
 public float velocitySpeed = 0f;

 public float jumpHeight = 5f;

 private float rayHeight = 1.1f;//ray is raycast down towards the ground, to check if player grounded
 
 private bool isGrounded;
 public bool isFlying;//testing to see if the player is walking or flying


 private Rigidbody rigid;



 // Start is called before the first frame update
 void Start()
 {
     rigid = gameObject.GetComponent<Rigidbody>();
 }

 // Update is called once per frame
 void Update()
 {

     int layerMask = 1 << 9;
     layerMask = 9;

     RaycastHit hit;
     Ray ray = new Ray(transform.position, -transform.up);
     Physics.Raycast(ray, out hit, rayHeight, layerMask);

     Debug.DrawRay(ray.origin, ray.direction * rayHeight, Color.red);

     if (hit.collider)
     {
         Debug.Log("Hitting Collider");
         isGrounded = true;
         isFlying = false;
     }
     else if (!hit.collider)
         isGrounded = false;


     if (isGrounded)
     {
         if (Input.GetKeyDown(KeyCode.Space))
         {
             rigid.AddRelativeForce(new Vector3(0,jumpHeight), ForceMode.Impulse);
             
         }
     }

     if (!isGrounded)
     {
         if (Input.GetKeyDown(KeyCode.Space))
         {
                isFlying = true;
         }
     }

     if (!isFlying)
     {
         rigid.useGravity = false;

         float translationZ = Input.GetAxis("Horizontal") * moveSpeed;
         float translationX = Input.GetAxis("Vertical") * moveSpeed;

         translationZ *= Time.deltaTime;
         translationX *= Time.deltaTime;


         transform.Translate(translationX, 0, translationZ);
     }


     if (isFlying)
     {
         rigid.useGravity = true;

         velocitySpeed = Mathf.Clamp(velocitySpeed, -0.1f, 0.1f);

         float translationZ = Input.GetAxis("Horizontal") * flySpeed;
         float translationX = Input.GetAxis("Vertical") * flySpeed;
         float translationY = Input.GetAxis("Jump") * +velocitySpeed * Time.deltaTime;

         translationZ *= Time.deltaTime;
         translationX *= Time.deltaTime;

         bool increaseHeight;
         
         if (Input.GetKeyDown(KeyCode.Space))
         {
             increaseHeight = true;
            
             if (increaseHeight)
             {
                 velocitySpeed += 0.1f;
             }
         }
         if (Input.GetKeyUp(KeyCode.Space))
         {
             increaseHeight = false;
             if (!increaseHeight){
                 velocitySpeed = 0f;
             }
         }

         if (Input.GetKeyDown(KeyCode.LeftShift))
         {
             increaseHeight = true;

             if (increaseHeight)
             {
                 velocitySpeed -= 0.1f;
             }

         }
         if (Input.GetKeyUp(KeyCode.LeftShift))
         {
             increaseHeight = false;

             if (!increaseHeight)
             {
                 velocitySpeed = 0f;
             }

         }
         transform.Translate(translationX, velocitySpeed, translationZ);




     }

 

 }

}