rb.AddForce(0, 0, forwardForce * Time.deltaTime);

    if (Input.GetKey("d"))
    {
        rb.AddForce(sidewaysForce * Time.deltaTime, 0, 0, ForceMode.VelocityChange);
    }

    if (Input.GetKey("a"))
    {
        rb.AddForce(-sidewaysForce * Time.deltaTime, 0, 0, ForceMode.VelocityChange);
    }