Tuning fork having 2 arms 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

 A: 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.
