Do you mean with only balances? With scales you would just weigh each bag once and sort the weights. In either case, why would bubble sort be preferred? I'd think you would want to minimize how many times you have to move the bags on and off the scale/balance.
A "Pair of scales" does mean the same as a "balance", but "scales" on its own sually means a device containing an electronic (or spring) weighing mechanism.
The problem goes something like this: You have N number of bags of the same size but different (maybe) weights. You have nothing to write and only balances. The easiest way to sort them is to put them in a row, compare them two by to and swap them in order.
