我按照了视频敲代码的，但是小球却一直无法移动，不知道哪里出错了

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

public class Player : MonoBehaviour{

    private Rigidbody rd;

    public int force = 5;

	// Use this for initialization
	void Start (){
      rd = GetComponent<Rigidbody>();
    }
	
	// Update is called once per frame
	void Update (){
      float h = Input.GetAxis("Horizontal");
      float v = Input.GetAxis("Vertical");
      rd.AddForce( new Vector3(h,0,v) * force );
	}
}