Science Buddies: "Ask an Expert"

Hi,
My daughter did the knock your blocks off experiment but did the “milk can “ portion of it only. We are having trouble explaining how the center of mass comes into play ( or if this is a balance issue) when only the top bottle is filled. If you calculate center of mass in this configuration it is near the top of the structure, however we were most successful by hitting the bottom bottles not the top one. Any ideas how we can explain this issue? Is it simply a balance and stability issue because the bottoms are empty?
Thanks for any help you can give us,
Anita and Alexis

Hi,

I'm not sure, but I believe that since the center of mass is near the top of the structure, hitting the bottom of the structure will be most effective because it destabilizes the structure, as the great amount of mass at the top will no longer have anything to support it. If any other experts have input, that would be great as well.