def calc_CdAm(frontal_area, mass):
    """Calculate drag term

    Args
    ----
    frontal_area: float
        Frontal area of animal
    mass: float
        Total animal mass

    Returns
    -------
    CdAm: float
        Friction term of hydrodynamic equation

    References
    ----------
    Miller, P.J.O., Johnson, M.P., Tyack, P.L., Terray, E.A., 2004. Swimming
    gaits, passive drag and buoyancy of diving sperm whales Physeter
    macrocephalus. Journal of Experimental Biology 207, 1953–1967.
    doi:10.1242/jeb.00993
    """
    Cd = 1.06
    return Cd * frontal_area / mass