@lynn As a schoolboy I worked with a cast-off LACE MK II analogue computer. Which was valve based, and had big power supplies with very large capacitors. My little brother discovered that if you took a spare one of these, and clamped its terminals in a stand nicked from the chemistry lab, and then put 6.3v AC at many, many amps across the terminals from one of the computer's massive valve heater transformers, the capacitor can would shoot right across the school playground.