Observations and results
When the pyramid was arranged with two empty bottles on the bottom (and a filled bottle on top), did it fall over the easiest? Was hitting the bottom bottles typically the best approach?
A lot of people may initially think that the center of mass of the first bottle pyramid you made is in the middle of the structure (where the upper bottle rests on the lower ones). But in this configuration, with all of the bottles filled equally, it's actually closer to the middle of the two bottom bottles—because there are two bottles on the bottom, there is more mass on the bottom of the pyramid than the top. So the center of mass is closer to the pyramid's bottom. In the second pyramid arrangement the center of mass became even lower because more mass was in the bottom part of the pyramid compared with the top. In the third pyramid arrangement the center of mass became much higher—somewhere within the top bottle.
You should have found that the third pyramid, with its higher center of mass, was the easiest one to knock over and most unstable, likely having all three bottles fall over when the ball touched any of them. On the other hand, the second pyramid, with its lower center of mass, was likely the hardest to knock over completely. In general, hitting the lower area between the bottom bottles (below the center of mass of the pyramid) should have been the most successful approach for knocking down the entire pyramid. Except for the third pyramid, hitting the top bottle likely only knocked the top bottle off of the pyramid, leaving the two others still standing.
More to explore
The Scientific Method & Carnival Games, from Portage, Inc.
Center of Mass, from High School Online Collaborative Writing
Fun, Science Activities for You and Your Family, from Science Buddies
Knock Your Blocks Off: The Mechanics of Carnival Games, from Science Buddies
This activity brought to you in partnership with Science Buddies