Unity c# -刚体.AddForce没有按预期工作

所以，我试图用WSAD按钮移动一个立方体，由于某种原因，即使我没有触摸任何按钮，它也会沿对角线向上和向左移动。我使用Unity 4.5.1

代码:

using UnityEngine;
using System.Collections;
public class Movement : MonoBehaviour {
    public float moveSpeed;
    private Vector3 input;
    // Use this for initialization
    void Start () {
    }
    // Update is called once per frame
    void Update () {
        input = new Vector3(Input.GetAxis ("Horizontal"), 0, Input.GetAxis ("Vertical"));
        print(input); 
    }
}