By DXS Biology Editor Jeanne Garbarino
Do you remember that old candle experiment involving a lit candle in a jar? You know, the one where you place a lit candle in a bowl of water, then place a jar over the candle, and rather quickly, the candle extinguishes? If you were like me, you probably learned that the candle goes out because all of the oxygen gets used up (oxygen is a requirement for combustion). However, according to David Isaac Rudel in his multi-volume series Science Myths Unmasked, this is one of the many science demonstrations that are wholly misinterpreted.
Unfortunately, the science textbooks used by thousands of schools across the US are chock-full of what Rudel calls “pseudo-explanations” for many complicated scientific phenomena. Instead of presenting clear explanations, including the establishment of a basic scientific foundation, many science textbooks present certain concepts using shortcuts, with the assumption that these so-called shortcuts make it easier for kids to understand science.
Rudel argues that these shortcuts, which are often associated with an “abuse of [scientific] language,” only confuse students. In fact, included on the back cover of Science Myths Unmasked, Volume 2: Physical Sciences is a quote from Richard Feynman regarding science textbooks: “They said things that were useless, mixed-up, ambiguous, confusing, and partially incorrect. How anybody can learn science from these books, I do not know, because it’s not science.”
My husband, a public high school chemistry and biology teacher, is wholeheartedly aligned with this particular opinion of Feynman and Rudel and for many years, has not used a textbook to teach science. When I asked why, he simply stated, “They just confuse the kids.”
As an example to what is wrong with science textbooks, let’s get back to the candle-in-a-jar experiment. In Science Myths Unmasked Volume 2: Physical Science, this very common scientific demonstration is thoroughly dissected, explaining why “the candle goes out when the oxygen content of the air is no longer high enough to support combustion” is an incorrect conclusion found in many textbooks, especially since it overlooks how the products of combustion affect the candle flame. After elaborating on the precise conditions point by point, and providing an outline for easy demonstrations to “expose the myth,” the following is stated:
Candles in closed containers do not go out because they use up all the oxygen. Rather, the hot carbon dioxide (and to a lesser extent water vapor) given off in combustion accumulates at the top, pushing down other gases (most importantly, oxygen), and eventually stifles the flame.
If the jar’s rim is submerged in water, the liquid rises not because water is replacing the oxygen used up in combustion. Rather, the air inside the jar cools as the flame dies down and hot gases offload heat to the glass container. As the air cools, it applies less pressure to the water than it did when the jar was first put over the candle. The water rises as a result of the decreasing pressure from the air against it.
In the Science Myths Unmasked series, a great number scientific factoids and processes that are often misrepresented in the classroom are correctly explained, and in great detail. In addition to the candle experiment described above, Rudel tackles simple machines, circuits, phase change, and waves, just to name a few. However, this book is not for those without at least some background in science, as it does get technical. I would, though, recommend that these books find a way onto the shelves of science educators, as it seems they would benefit the most from the lessons and demonstrations covered. It is also good for people who, like me, have a scientific background and wish to properly explain scientific concepts to their kids, as I am sure those questions are bound to come up.
For more on the Science Myths Unmasked series, go here.