How many times has a soda can exploded all over you? Some people (myself included) like to vigorously tap the can before opening, in order to minimize spray. Does this handy "trick" really work? Read this article to see an experiment involving exploding soda cans.
This article outlines an experiment examining the tapping of soda cans. The experiment involved three groups. For each group, the soda can was shaken. In the first group, the can was opened right after the shaking. The second group's can was opened after ten seconds. Finally, the third group's can was tapped for ten seconds, and then opened. This experiment was repeated three times total. Surprisingly, the experimenters did not find a convincing correlation between tapping and amount of spray. The tapped can expelled slightly less spray than the other two, but there was not a great difference between the settled second can and the tapped third can. Thus, it seems that tapping soda cans is not a very effective activity.
We should look for Rival Hypotheses in this experiment. A major flaw in this experiment is the lack of separation between two important variables-- the settling of the can and the tapping of the can. The cans in the third group of the experiment both settle AND are tapped. To correct this in a future experiment, researchers should introduce a fourth group. In this group, the can should be vigorously tapped for one to three seconds, and then opened. This would allow researchers to focus on the tapping element without the settling element. In summary, this confound introduces a rival hypothesis. Is the can spewing less liquid because of the tapping, or because of the settling? The results seem to indicate that the settling of the can, not tapping, is the crucial variable, but it is still very important to analyze this further.
In conclusion, it seems that tapping a soda can does not really reduce the amount of spray from a carbonated can. Instead, the can should sit and settle for a minute or two. While it may seem that tapping the can will reduce the likelihood of an explosion, this is probably due to our availability heuristic-- we recall more easily the times when we DID NOT tap the can and it exploded than we remember all the times we DID tap the can, and it DID explode.