public Vector3 position { get; set; }

_position allows you to get and set the position of a Rigidbody using the physics engine. If you change the position of a Rigidbody using _position, the transform will be updated after the next physics simulation step. This is faster than updating the position using _position, as the latter will cause all attached Colliders to recalculate their positions relative to the Rigidbody.

If you want to continuously move a rigidbody use Rigidbody.MovePosition instead, which takes interpolation into account.

using UnityEngine;using System.Collections;public class ExampleClass : MonoBehaviour{    void Start()    {        GetComponent<Rigidbody>().position = Vector3.zero;    }}