Unity Editor-only helper script to simulate gravity for placing objects on ground with physics

SimulateGravity.cs

#if UNITY_EDITOR
using System.Collections;
using UnityEditor;
using UnityEngine;

[ExecuteInEditMode]
public class SimulateGravity : MonoBehaviour
{
    public bool simulate = false;
    public bool remove = false;
    new Rigidbody rigidbody;

    private void OnValidate()
    {
        rigidbody = GetComponent<Rigidbody>();
        if (!rigidbody) Debug.Log("Cannot simulate gravity without a rigidbody");
        if(!simulate && !remove) StartCoroutine(SimulateCoroutine());
    }

    void Update()
    {
        if(remove)
        {
            Physics.autoSimulation = true;
            DestroyImmediate(this);
        }
        if (!simulate) return;
        Physics.autoSimulation = false;
        Physics.Simulate(Time.deltaTime);
    }
    [MenuItem("Tools/SimulateGravity")]
    public static void StartSimulateGravity()
    {
        Rigidbody selectionRigidbody = Selection.activeGameObject.GetComponent<Rigidbody>();
        if (!selectionRigidbody)
        {
            Debug.LogError("Cannot simulate gravity on a gameobject without a rigidbody");
            return;
        }
        Selection.activeGameObject.AddComponent <SimulateGravity> ();
    }

    IEnumerator SimulateCoroutine()
    {
        simulate = true;
        yield return new WaitForSeconds(1f);
        simulate = false;
        remove = true;
    }
}
#endif