Found this on Whirlpool:
There are 8 balls and a set of balance scales, all the balls are the same size and shape but one of them is heavier than the others.
How can we get the heaviest ball with the fewest number of weights?
First answer:
Two packs of four on the balance, discard lightest four.
Two packs of two, discard lightest two.
Two balls, discard lightest.
Second (better) answer:
Take two lots of three balls and compare them. If they are the same, compare the remaining two to see which is heavier. If one set of three is heavier, compare two of those. If they are different, take the heaviest one. Otherwise the one of the three you did not compare will be the heavier one.