Gyroscope.userAcceleration

Description

Возвращает ускорение, которое пользователь задал устройству.

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.

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);
    }
}