def evaluaterforces(Pot,R,z,phi=None,t=0.,v=None):
    """
    NAME:

       evaluaterforces

    PURPOSE:

       convenience function to evaluate a possible sum of potentials

    INPUT:

       Pot - a potential or list of potentials

       R - cylindrical Galactocentric distance (can be Quantity)

       z - distance above the plane (can be Quantity)

       phi - azimuth (optional; can be Quantity)

       t - time (optional; can be Quantity)

       v - current velocity in cylindrical coordinates (optional, but required when including dissipative forces; can be a Quantity)

    OUTPUT:

       F_r(R,z,phi,t)

    HISTORY:

       2016-06-10 - Written - Bovy (UofT)

    """
    isList= isinstance(Pot,list)
    nonAxi= _isNonAxi(Pot)
    if nonAxi and phi is None:
        raise PotentialError("The (list of) Potential instances is non-axisymmetric, but you did not provide phi")
    dissipative= _isDissipative(Pot)
    if dissipative and v is None:
        raise PotentialError("The (list of) Potential instances includes dissipative, but you did not provide the 3D velocity (required for dissipative forces")
    if isList:
        sum= 0.
        for pot in Pot:
            if isinstance(pot,DissipativeForce):
                sum+= pot.rforce(R,z,phi=phi,t=t,v=v,use_physical=False)
            else:
                sum+= pot.rforce(R,z,phi=phi,t=t,use_physical=False)
        return sum
    elif isinstance(Pot,Potential):
        return Pot.rforce(R,z,phi=phi,t=t,use_physical=False)
    elif isinstance(Pot,DissipativeForce):
        return Pot.rforce(R,z,phi=phi,t=t,v=v,use_physical=False)
    else: #pragma: no cover 
        raise PotentialError("Input to 'evaluaterforces' is neither a Potential-instance or a list of such instances")