GamesNovatory/Devices/Balances/Finding The Faulty Coin

Origin of the Game
Given 9 coins and a balance, how does one find the faulty coin (which weighs more than the others) using the balance only twice ?


The Device
Most kindergarten and elementary classes are equipped with a rudimentary balance,
     the problem being to make the weights, which will represent the coins.
We recommend using small containers, like those used for 16mm film,
     the empty container serving as the authentic weight,
          with a little plasticene added for the faulty piece.

With small children, you might prefer to start with only 3 pieces
(including the faulty piece, of course).
They have very little choice but to put 1 on each side,
and, if the balance is even, the faulty piece is the one left over.

Once the division in 3 equal groups is established,
working with the 9 pieces should not be too difficult.