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Why there is 2 arms in the tuning fork? It can have 1 or more than 2 arms. If we think to create more resonance, then we can construct a tuning fork having many arms enter image description here

sammy gerbil
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user157918
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    Great video that explains this https://www.youtube.com/watch?v=m7xUtR2qevA – YoA Jun 01 '17 at 18:22
  • I could also make a car with 5 wheels, but why? – Shufflepants Jun 01 '17 at 21:20
  • Is it only me who sees an interesting question here - is it possible to create a chord (of two or three tones) with a single piece of metal? I think not with the single piece of metal, but it comes me a nice question.... – jaromrax Jun 02 '17 at 11:40
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    @jaromrax: you could ask this as a question... but yes, it is. Bells, for instance ring with frequencies which are not simply multiples of each other. –  Jun 02 '17 at 14:53

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Having two arms helps you hold a tuning fork without damping it, which in turn makes it usable.

If you consider a single-armed tuning fork -- just a metal bar really -- then such a thing clearly can ring in the way a tuning fork does. But unless you hold the thing by a node (which will be some inconveniently small point about a third of the way along it in the lowest mode) then when you hold it you will damp the vibration. A tuning fork with two arms, on the other hand, is 'balanced' to first order: the arms vibrate in opposing directions, and the stem of the fork is, to a good first approximation, completely stationary. That means that you can hold the thing by its stem (or that you can mount the tuning fork in a holder &c &c) without significantly damping it. This makes a tuning fork actually usable for, well, tuning things, since you need it to ring for several seconds (ideally ~10 seconds) in order to tune an instrument.

You could probably imagine tuning forks with more than two arms -- even numbers would be preferred I think -- but there is no purpose to such a thing: two is enough, and is easy to make.