Code: Rotation Speed

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CoinController : MonoBehaviour {

//Set up how fast your coin will rotate
public float rotationSpeed = 100;
// Update is called once per frame
void Update ()
{
//Tell Unity how to make the coin rotate
float angleRot = rotationSpeed * Time.deltaTime;
//Ask your Coin to rotate
transform.Rotate (Vector3.up * angleRot, Space.World);
}
}