我仍在学习，大家是否明白为什么我的脚本不起作用？

using UnityEngine;

public class Falling_ball : MonoBehaviour
{
private Rigidbody2D _rigidbody;

private void Awake()
{
    // 在启动时使物体静止
    _rigidbody.bodyType = RigidbodyType2D.Static;
}

void OnCollisionEnter2D(Collider2D other)
{
    // 检测玩家是否与物体接触
    if (other.CompareTag("Player"))
    {
        Debug.Log("玩家接触了这个球");

        // 获取球体的组件并变为动态
        Rigidbody2D rb = GetComponent<Rigidbody2D>();
        rb.bodyType = RigidbodyType2D.Dynamic;
    }
}

}