Often people think that the direction of the magnetic field in the coil determines the direct of force that acts on the core. This is not true. The core is ferromagnetic (and not a permanent magnet with defined poles), therefore the core will always be attracted to the centre of the magnetic field. Both coils for AC and DC pull the core towards the centre. It doesn't matter how the coil is connected to the power supply (the poles can be connected both ways).