# ***************************************************************************
# *   Copyright (c) 2020 Bernd Hahnebach <bernd@bimstatik.org>              *
# *                                                                         *
# *   This file is part of the FreeCAD CAx development system.              *
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# *   it under the terms of the GNU Lesser General Public License (LGPL)    *
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""" Collection of natural constants for the Fem module.

This module contains natural constants for the Fem module.
All constants are in SI units.
"""


__title__ = "Constants"
__author__ = "Bernd Hahnebach"
__url__ = "http://www.freecadweb.org"


def gravity():
    return "9.82 m/s^2"


def stefan_boltzmann():
    return "5.67e-8 W/(m^2*K^4)"


def vacuum_permittivity():
    # https://forum.freecadweb.org/viewtopic.php?f=18&p=400959#p400959
    return "8.8542e-12 s^4*A^2 / (m^3*kg)"


def boltzmann_constant():
    return "1.3807e-23 J/K"


"""
from FreeCAD import Units
from femtools import constants
Units.Quantity(constants.gravity()).getValueAs("mm/s^2")

"""

# TODO: a unit test to be sure these values are returned!