Adds a force to the rigidbody. As a result the rigidbody will start moving.

	// Adds a force upwards in the global coordinate system
	function FixedUpdate () {
		rigidbody.AddForce (Vector3.up * 10);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void FixedUpdate() {
        rigidbody.AddForce(Vector3.up * 10);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def FixedUpdate() as void:
		rigidbody.AddForce((Vector3.up * 10))

Adds a force to the rigidbody. As a result the rigidbody will start moving.

	// Adds a force upwards in the global coordinate system
	function FixedUpdate () {
		rigidbody.AddForce (0, 10, 0);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void FixedUpdate() {
        rigidbody.AddForce(0, 10, 0);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def FixedUpdate() as void:
		rigidbody.AddForce(0, 10, 0)

If you want to apply a force over several frames you should apply it inside FixedUpdate instead of Update.