An oscillator from a jam-jar lid
Fiddling with a jam-jar lid suggested its tamper-evident pop-up button exhibited hysteresis, and so I did some experiments on a blackcurrant jam lid to test this. Adding weight 50g at a time, the lid flexes very slightly, but stays popped up with 800g on top. It pops down when you add 50g to make 850g. Removing weight 50g at a time, the lid does not pop back up straight away. It stays down as you decrease the weight to 650g, but when you remove 50g to leave 600g, it pops back up. This confirms the suspected hysteresis. I read a long time ago that if you take a system with hysteresis, and introduce negative feedback from the response to the
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