Click and drag - Object go through other objects when dragging

Hello,

I created a script with which you can drag objects, but when I drag an object it doesn't collide with other objects and go through them... Here's the code:

 var speed:float;
 var target : Vector3;
 var start : Vector3;
 private var pos;
 var self : GameObject;
 var distanceToObject : float = 7.5;
 var dragging : boolean = false;
  
 function Start()
 {
     start = transform.position;
     pos = transform.position;
 }
  
 function Update ()
 {
     if(Input.GetMouseButtonDown(0))
     {
     var ray = Camera.main.ScreenPointToRay(Vector3(Screen.width * 0.5, Screen.height * 0.5, 0.0));
     var hit : RaycastHit;
     if(Physics.Raycast(ray, hit, distanceToObject))
     {
     if(hit.collider.gameObject == self)
     {
        Destroy(self.GetComponent(Rigidbody));
        dragging = true;
     }
     }
     }
     if(Input.GetMouseButtonUp(0)) {
         if(dragging) {
         self.AddComponent(Rigidbody);
         dragging = false;
         }
     }
     if(dragging) {
         pos = Input.mousePosition;
         pos.z = 3.5;
         pos = Camera.main.ScreenToWorldPoint(pos);
         transform.position = Vector3.Lerp(transform.position, pos, speed*Time.deltaTime);
     }
 }

What should I do?

Also you need to add this if you want it to work right:

 function Start() {
 Screen.lockCursor = true;
 }