Weighing puzzle........

This is one gem, that I got from a friend of mine. The puzzle in its simplest form goes like this:

There are a set of 8 balls. Out of which 7 are of same mass, and the remaining one is heavier than the rest. What is the minimum number of weighings required to find out the heavier ball? i.e. How many times do you require to use the balance?

Try to solve this puzzle at ur best........i will tell u the answer on monday.Let me see hw many of u r the real challenger's.........