Great question! After doing some research, I
have some evidence for you: here's a video that
supports the idea that
tapping the sides of a soda can minimizes
explosions . (But note that this video is
not a real science experiment, because they did
not use a control group. They should have
tested what happens if you shake a soda can and
open it without tapping. After all, not all
types of soda cans are the same--maybe none of
the ones they tested could explode anyways!)
As they mention in the video, scientists think
that the explosions are caused by bubbles of
carbon dioxide gas. Where do these bubbles come
from and what do they do?
Soda cans are sealed using special machines. These
machines pump carbon dioxide into the can, then
trap it under the lid. This gives the inside of
the can a high pressure. Normally, most of the
carbon dioxide sits on top of the liquid. But if
you shake the can, some of the carbon dioxide gets
trapped in bubbles instead. Most of these
bubbles stick to the inside wall of the can.
When the can is opened, the pressure inside
will be released, causing the bubbles to rise and
expand. As the bubbles rise, they carry some of
the soda up and out of the can.
Before you open the can, if you tap on the
sides, you can knock the bubbles off the walls.
The idea is to put all of the carbon dioxide
back above the liquid. Then when you open the
can, the pressure can escape without disturbing
the liquid below!
By the way, it seems that this strategy works
better on some types of soda than on others.
It's possible that the bubbles in some types of
soda are harder to dislodge than others. Some
types of soda may have chemicals in them that
increase bubble formation. But I haven't tested
this theory, so I can't say for sure.
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