dash till puff game

hey ... i am trying to make dash till puff game just for training .. but i have a problem ..

in the game when i touch the screen i can move up when i release it i can move down ...

i feel no forces when i play it

all i did just it can jump when i press "W" key in that code below ......

 using UnityEngine;
 using System.Collections;
 
 public class player_control : MonoBehaviour {
 
     Rigidbody2D rb2d;
     public float speed = 1.0f;
     // Use this for initialization
     void Start () {
         
         rb2d = gameObject.GetComponent<Rigidbody2D>();
 
     }
     
     // Update is called once per frame
     void Update () {
     
         if(Input.GetKey("w")){
         
             rb2d.velocity =  (new Vector2 (0, speed));
     
         
         }
     
     }
 }
 

i don't want that .... it should fly not jump

and here is all physics i added to the ball

so any ideas ??