def _force(**kwargs):  # {{{
    """
    Determine the force. See Load.__init__()

    Returns:
        The force as a float.

    Examples:
        >>> _force(kg=1)
        -9.81
    """
    if "force" in kwargs:
        force = float(kwargs["force"])
    elif "kg" in kwargs:
        force = -9.81 * float(kwargs["kg"])
    else:
        raise KeyError("No 'force' or 'kg' present")
    return force