Gyroscope.userAcceleration

Description

Returns the acceleration that the user is giving to the device.

The significance of this value is that the effect of gravity (which is also detected by the accelerometer) has been removed to leave just the acceleration from the user's movements.

var forceVec: Vector3;
var rb: Rigidbody;

function Start() {
    rb = GetComponent.<Rigidbody>();
}

function FixedUpdate() {
    // Apply forces to an object to match the side-to-side acceleration
    // the user is giving to the device.
    rb.AddForce(Input.gyro.userAcceleration.x * forceVec);
}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public Vector3 forceVec;
    public Rigidbody rb;
    void Start() {
        rb = GetComponent<Rigidbody>();
    }
    void FixedUpdate() {
        rb.AddForce(Input.gyro.userAcceleration.x * forceVec);
    }
}