Adding Accelerating to a Wheel of fortune

Basically I want to create a wheel of fortune where user turn the wheel by actually clicking and dragging the wheel (like real wheel of fortune). The problem is I don’t know how to add an acceleration to it base on how fast the user drag the wheel and also adding friction to slow it down. something similar to this: https://youtu.be/x6wOjk5AwZQ?t=3m34s

here is my code: using UnityEngine; using System.Collections;

 public class RotateWheel : MonoBehaviour
 {
     private float baseAngle = 0.0f;
 
     void OnMouseDown()
     {
         var dir = Camera.main.WorldToScreenPoint(transform.position);
         dir = Input.mousePosition - dir;
         baseAngle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg;
         baseAngle -= Mathf.Atan2(transform.right.y, transform.right.x) * Mathf.Rad2Deg;
     }
 
     void OnMouseDrag()
     {
         var dir = Camera.main.WorldToScreenPoint(transform.position);
         dir = Input.mousePosition - dir;
         var angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg - baseAngle;
         transform.rotation = Quaternion.AngleAxis(angle, Vector3.forward);
     }
 }

any help is much appreciated :)