This function is called every fixed framerate frame, if the MonoBehaviour is enabled.

FixedUpdate should be used instead of Update when dealing with Rigidbody. For example when adding a force to a rigidbody, you have to apply the force every fixed frame inside FixedUpdate instead of every frame inside Update.

	// Apply a upwards force to the rigid body every frame
	function FixedUpdate () {
		rigidbody.AddForce (Vector3.up);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void FixedUpdate() {
        rigidbody.AddForce(Vector3.up);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def FixedUpdate() as void:
		rigidbody.AddForce(Vector3.up)

In order to get the elapsed time since last call to Update, use Time.deltaTime This function is only called if the Behaviour is enabled. Override this function in order to provide your component's functionality.