touch control and Box Collider2D

Do not "move" physics stuff with the Transform. That is what the Rigidbody2D is for so use its API. By changing the Transform you're simply instantly changing the location of a Rigidbody2D/Collider2D and it bypasses the primary reason for adding a Rigidbody2D which is to write poses to the Transform system.

If you've not added a Rigidbody2D then that's even worse. This means you've added a Collider2D and it's implicitly static (non-moving) yet you're constantly and instantly changing it's position.

You're also using "Time.deltaTime" rather than "Time.fixedDeltaTime" but you're lucky (and I don't personally like this feature) because during FixedUpdate, Unity returns fixed-time when you read deltaTime because it assumes that what you actually meant.

 

Np. If I helped then a like is all I ask.

 

If you're just starting with 2D physics then go watch a few starter tutorials like these: https://learn.unity.com/search/?k=["tag:5813f57532b30600250d6e0d","lang:en","q:2d+physics"]

Don't use Transform to manipulate physics. If something is moving in physics, it's moving because you added a Rigidbody2D. It writes the position and rotation to the Transform for you. You talk directly to the Rigidbody2D by doing things like adding forces, setting velocity or asking it to move to a position or rotation.

Try something ilke this instead but note I've not tested this and it's not the best way to move stuff:

Code (CSharp):

1.  
2. using System.Collections;
3. using UnityEngine;
4.  
5. using System.Collections;
6. using UnityEngine;
7.  
8. public class InputTouch : MonoBehaviour
9. {
10.     public float TouchSpeed = 0.3f;
11.  
12.     void FixedUpdate()
13.     {
14.          #if UNITY_ANDROID  
15.          if (Input.touchCount > 0 )
16.          {
17.              var rb = GetComponent<Rigidbody2D>();
18.              var touchOffset = Input.GetTouch(0).deltaPosition * TouchSpeed * Time.fixedDeltaTime;
19.              var targetPosition = targetPosition.position + touchOffset;
20.              rb.MovePosition(targetPosition);
21.           }              
22.          #endif
23.     }
24. }

Take a look at my profile below, download the GutHub project and load-up the MouseDrag scene. It shows you how to drag stuff using the mouse but can equally be done with any pointer device. It uses a TargetJoint2D and you can set how quickly it follows etc.

Anyway, It looks like this: