The spring that connects two equal pendulums in a conventional coupled pendulums demonstration is replaced here by a thread, with a small weight in the middle of it. A horizontal pen, attached to this weight, writes the trace of the weight on a vertical piece of paper. The (equal) bobs (1.5 kg) are suspended from the ceiling with nylon threads (250 cm, i.e. T ~ 3.15 sec), 120 cm apart; the connecting thread (160 cm) is attached to the pendulums (with clips) 90 cm above the weights; it carries a weight (15 g
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