Ring Launcher AC vs DC?

[nsled]

Why does an AC launch a ring much further than DC? It's demonstrated here but not explained;

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I believe that example is just using mains AC/rectified DC. Would a capacitor discharge into the coil result in the AC or DC effect?

[dexter]

Current is induced into the ring only when the magnetic flux changes. In the DC experiment that happens when the switch either closes or opens, so the ring will not move that much. When AC is applied the long iron core the coil and the ring is a induction motor.

A capacitor discharge into the coil result in the DC effect.

[FPS]

I was thinking the DC pulse would resonate with the capacitor in effect operating as an AC pulse.

So why do the flat launchers not use an iron core as well? like this one doesn't.

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There's plenty of examples online but every capacitor driven launcher has no iron core, every AC mains one does have an iron core. I guess I'm looking for the reason, if any.

[MRMILSTAR]

I can think of several reasons. The AC induction launcher uses a long solenoid-type coil excited by continuous 60 Hz AC. The iron core serves to concentrate the magnetic flux. The energy applied to the ring is added continuously along the length of the coil. If DC were applied, energy would only be added for the duration of the damped sinusoid response. In this case the damped sinusoid duration and frequency would be determined by the coil inductance and parasitic capacitance of the coil. The duration would be considerably shorter than the length of the coil thus making continuous AC much more effective.

For the case of a disc launcher, the coil is flat and the disc is in almost direct contact with all of the coil. The capacitor discharges all of its energy into the coil within a few microseconds. The waveform shape is that of a damped sinusoid caused by the resonance of the capacitor/coil combination. My launcher has a resonant frequency of about 7500 Hz. At frequencies that high, an iron core is unnecessary and would be very lossy.