Transform.up 向上

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
	public void Awake() {
		rigidbody.velocity = transform.up * 10;
	}
}

// Set's the rigidbody velocity to be
// along the green axis of the transform
//设置刚体的速度沿着物体的绿色轴移动
rigidbody.velocity = transform.up * 10;