Balancing Soda Can
Eva Rosenberg
Award: Top 100
School: montgomery blair high school
Teacher: matthew jacobs
Category: Contrived
Photo #19178
Balancing Soda Can
One time, I saw a video of someone balancing their soda can on a tilt. He said you had to drink
about half of the can, and then it would balance. I tried this and indeed, the bottle was still
standing.
Now, why does this work? Why can a single sip make the difference between the can standing
or falling? It is because of the center of mass. Every object has one, it's the point where all of
the weighted position vectors are balanced. In 3D space, there are three axes, and the center of
mass can be calculated by adding the weight at every position along each axis and dividing by
the total mass of the system. An object balances when its center of mass is above its base of
support. So, the can doesn't balance because it's halfway empty, it balances when the center of
mass is directly over the small dent in the bottom. That's why one sip can make or break it, the
base of support in this case is very narrow. And it's why longer cans often can't do this. A
majority of their mass is over the base of support, and the liquid inside can't shift the center of
mass enough to stay balanced.
Now every time I drink a standard 12 oz can of soda, I particularly look forward to reaching the
halfway point, because I can balance it on the edge, which looks cool, and makes others ask,
"How'd you do that?"
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