Annals of Improbable Research, Special Physics Issue

Question: Produce your favorite short list of seemingly mundane physics questions that seem, so far, too hard for anyone to have solved. These should be about phenomena that ANYONE can see in everyday life.

1. Does your chewing gum lose its flavor on the bedpost overnight?

It seems that this is a simple physics question of the rate of diffusive loss of menthol or other flavor molecules trapped in a high molecular weight gum, but appearances are deceptive. The flavor often reappears if a sweet drink is taken before recommencing chewing. It was there all the time, but the brain needed the sweetness cue to notice. The brain is, of course, a complicated electrical circuit, and it is the performance of this circuitry that is the real physics mystery.

2. Why are pubic hairs thicker than the hairs on the head?

This is presumably because of the different requirements for heat insulation in the respective parts of the body, either now or at some time in the distant past, but so far as I know there has never been a systematic thermographic study. A grant application is in progress.

3. How does water reach the leaves of a tree?

So far as the botany textbooks are concerned, this one is solved, since the height to which water will rise by capillary action is determined solely by the diameter of the capillary at the meniscus. If the capillary has a diameter of 1μm at this point, for example, the resultant capillary pressure can support a column of water 20 meters high, no matter how wide the rest of the column may be.

In trees, the menisci are within the leaves, and such menisci can have diameters of much less than 1μm, which apparently accounts for the height to which trees can grow. However (as anyone who has ever listened to a tree with a stethoscope will know) the columns of water that flow up the xylem are forever breaking (producing audible clicks). The breaks occur at places where the diameter is much greater than 1μm, and the meniscus at this point can no longer support the liquid column below, which rapidly drains away. Once a column has broken, there is no way for it to re-form. Over time, all columns must break, and the tree should then die of dehydration.

4. Why is hair conditioner ineffective on the second day when used on successive days?

Studies on the hair of a group of Siberian nuns who only wash their hair in water have shown that hair conditioners spread to form a uniform coat on fresh hair. A single drop of polydimethylsiloxane, a major component of hair conditioners, similarly spreads on water to form a thin film. A second drop, however, fails to spread. This phenomenon presumably accounts for the ineffectiveness of hair conditioners when applied to hair from which previous conditioner has not been removed, but the phenomenon itself remains unexplained.

5. How does spinning keep your balls down?

There are some plastics, often made into balls or other toys, that have a density only slightly less than that of water, and which will slowly float upwards when pushed to the bottom of a container of water and released. If the same experiment is performed with the container of water rotating (e.g. by putting it on an old-fashioned record player) the ball will either fail to rise or rise more slowly. It seems to be a very simple problem, but no-one to my knowledge has yet produced a satisfactory explanation.

6. How much water comes out of a hose?

Or, more generally, how much water comes out of a pipe of given dimensions for a given viscosity and pressure gradient which exceed the conditions for laminar flow? The answer to this question is, as far as I know, only known empirically.

7. How is it possible to open a bottle of wine without a corkscrew?

Bang the base of the bottle against a tree a number of times, and the cork will come out. Physicists who have tried this are convinced that they should be able to explain it, but have never yet been sober enough to put this assertion to the test.

I am grateful to my scientific colleagues, and in particular to Terry Cosgrove, Julian Eastoe, Jeff Odell and Rob Richardson of Bristol University, and Joe Wolfe from the University of New South Wales, for their contributions to my puzzlement. The discussions are my own, but any errors are, of course, theirs.

© This article is copyright Len Fisher. Please email Len Fisher to seek permission to reproduce part or all of the above article.

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