Lift the balls up to a height of around 1 m and let them drop freely. See how high they bounce.
How it works
When balls which fall together bounce back, the total mechanical energy and the total momentum of balls is conserved. Bouncing occurs in stages separated by very little time: rebounding of the heaviest the bottom ball from the ground and its collision as it moves upwards with the still falling middle ball, the collision of the middle ball already moving upwards with the still falling lightest top ball. In such a collision, the lightest top ball will gain extra energy at the expense of the other, heavier balls and, as a result, will bounce back to a greater height than the initial one.