a bowl of water and have it stay in the center. Fun-loving folks that they are, they'll probably take up the challenge, placing the cork ever more carefully in the center of the bowl, only to have it drift to the side again and again.
HOW TO DO IT:Very slowly add water to the bowl until the water level actually rises over the rim of the bowl in a wiggly curve (for extra points, explain to your parents that the water is held in place by surface tension). This time, when you gently set the cork in the water, it moves to the bowl's center, the place where the water level is highest. Since a little water may spill as you do this, you might want to put your bowl on a plate. (If you forget, explain to your parents that you've just demonstrated displacement.)
