Moving an object after player click?

Hello,
I have a script that slightly adds velocity which seems to work well but I still have the issue of consistently applying the force so the object keeps moving instead of just sliding forward a little. Any ideas on how to make it keep applying force instead of just pushing it once?

 void FixedUpdate()
    {
        if(Input.GetMouseButtonUp(0))
        {
            rb.velocity = new Vector2(1, 0);
        }

    }

public float LinearDrag = 1;
private Vector2 velocity;

 void Update()
 {
     if(Input.GetMouseButtonUp(0))
     {
         velocity = new Vector2(1, 0);
     }
     else if( velocity.x > Time.deltaTime * LinearDrag )
         velocity.x -= Time.deltaTime * LinearDrag;
      else
          velocity.x = 0;
 }

 void FixedUpdate()
 {
     rb.velocity = velocity;
 }