def deceleration(K, m, rho_atm, v):
    """ Computes the deceleration derivative.     
    Arguments:
        K: [double] Shape-density coefficient (m^2/kg^(2/3)).
        m: [double] Mass (kg).
        rho_atm: [double] Atmosphere density (kg/m^3).
        v: [double] Velocity (m/S).
    Return:
        dv/dt: [double] Deceleration.
    """

    return -K*m**(-1/3.0)*rho_atm*v**2