Physics.gravity

Description

The gravity applied to all rigid bodies in the scene.

Gravity can be turned off for an individual rigidbody using its useGravity property.

          Physics.gravity = Vector3(0, -1.0, 0);

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Example() {
        Physics.gravity = new Vector3(0, -1.0F, 0);
    }
}