Collision2D.relativeVelocity

Description

这两个碰撞对象的相对线性速度（只读）。

// Play a sound when we hit an object with a big velocity
using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    AudioSource audioSource;

    void Start()
    {
        audioSource = GetComponent<AudioSource>();
    }

    void OnCollisionEnter2D(Collision2D collision)
    {
        if (collision.relativeVelocity.magnitude > 2)
            audioSource.Play();
    }
}