You split the balls in 3 groups - 3, 3, 2.

1st weigh. On each side of the scale place 3 balls.

- If he groups are equal in weight, then w)eigh the 2 balls from the 3rd group => you'll have your answer in 2 steps (2nd weigh)

- If the 3-ball groups are not equal in weight, pick the heaviest.

2nd weigh: on each side of the scale place one ball from the previously chosen group of 3.

- if the balls are equal, the heaviest is the one that is left

-otherwise, the scale will tell you which ball is heavier.

Thus, you use the scale only 2 times. This is the minimum number of operations that has to be done.

split the 8 balls into 2 groups of 4. weight each group on each side of the scale. Discard the lighter side. Take the heavier group and split into 2 groups of 2. Discard the lighter side. Take the heavier group and split into 2 groups of 1. the heavier side is the heaviest ball.