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neRkP TIL that an acoustic piano has a tension string of almost 20 tons, because it has over 230 strings, and each string is under a tension of almost 90 kg (do the math). Because of this the piano is so heavy: because its iron-cast frame to withstand that tension.
rRxaW TIL that the collective tension of all the strings on a piano totals out at about 20 tonnes.