A false coin

A guy gives you 9 coins and says 'One coin is false, it's lighter than the other eight.'


You can use a balance several times and determine which coin is false. You are given a balance scale which lets you put the same number of coins on each side and observe which side (if either) is heavier. How many times do you need the balance to figure out which coin is false ?

7 8 9
4 5 6
1 2 3