Where the GetComponent based approaches automatically find the Rigidbody, this one exposes a field in the Inspector where you can manually assign it.

using UnityEngine;

public sealed class SerializeFieldExample : MonoBehaviour
{
    [SerializeField] private Rigidbody _Rigidbody;

    private void FixedUpdate()
    {
        _Rigidbody.AddForce(Vector3.up * 10);
    }
}

This concept is known as Dependency Injection; ths SerializeFieldExample class depends on a Rigidbody, but instead of finding or creating one, it simply indicates that it wants one and relies on another system to assign it (in this case, Unity's serialization system).

Advantages

• Fastest runtime performance - Unity deserializing the reference to set the field is faster than a script calling GetComponent on startup.
• The Inspector shows what other components the SerializeFieldExample depends on and which one is actually being used.
• The other components can be anywhere. The script isn't hard-coded with the assumption that the Rigidbody will be attached to the same GameObject.
• There's less code than the Get Component Cached and Require Component approaches, but a bit more than the original Get Component approach.

Disadvantages