Rigidbody.angularVelocity 角速度

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
	public Material fastWheelMaterial;
	public Material slowWheelMaterial;
	void Update() {
	if (rigidbody.angularVelocity.magnitude < 5)
		renderer.sharedMaterial = slowWheelMaterial;
	else
		renderer.sharedMaterial = fastWheelMaterial;
	}
}

// Change the material depending on the speed of rotation
//根据不同的旋转速度，改变这个材质

var fastWheelMaterial : Material;
var slowWheelMaterial : Material;
function Update () {
	if (rigidbody.angularVelocity.magnitude < 5) {
		renderer.sharedMaterial = slowWheelMaterial;
	}
	else {
		renderer.sharedMaterial = fastWheelMaterial;
	}
}