# STRANGE BUT TRUE- Potato fun: How to deal with broken wipers

DRAWING BY DEBORAH DERR McCLINTOCK

Q. On a drive with your savvy automotive engineering girlfriend, you encounter a light but steady rain when the windshield wipers on her old jalopy suddenly stop. Pulling over, she takes a potato out of her purse, slices it in half with a pen knife, and jumps out of the car. What's she up to this time? –D. Patrick

A. Unexpectedly, she starts vigorously rubbing the potato all over the windshield. Then, back on the road with visibility much improved, she begins regaling you with what she's done: "Visibility through a windshield decreases when water beads up on the glass, distorting your view through it," as told by Jearl Walker in The Flying Circus of Physics.

"But if you rub the exterior with a cut potato, the starch coating strongly attracts the rain molecules and spreads them out in a smooth layer," Walker says, "with visibility now reasonably clear."

Just be glad she didn't launch into how bird droppings on a car, especially from oily-fish-eating birds, help the rain spread out into thinner layers and dry faster around the spottings. Electrical utility companies know the phenomenon all too well as a buildup of such droppings can short out service lines and cause serious "flashover."

Q. Are you card player enough to know if "52!" is a very big or a very small number? –J. Cada

A. Let's make that a mathematical card player, because the ! symbol after the 52 denotes not surprise or excitement but the concept of "factorial." For example, "5 factorial" is the quantity 5 x 4 x 3 x 2 x 1, which equals 120; 10! Is 10 x 9 x 8... x 1, or 3,628,800. Many calculators in fact have a factorial button labelled "n!"

Factorials are useful for computing the number of ways a group of things can be arranged or ordered, such as 11! telling you how many different lines could be formed when a football team's 11 starting defensive players queue up for a beefing up at the buffet table after the game, amounting to about 40 million different permutations.

Finally, the card player's shuffle works to randomize the order of the 52 different cards, with the top one being any one of the 52, then the second card any one of the remaining 51, then 50, then 49, and so forth to the bottom of the deck. So make that 52! different ways the cards could wind up after shuffling, or 8 x 10 to the 67th power– a very big number indeed with 68 digits!

Q. Is it true you can stand a raw egg on end at the vernal or autumnal equinox? On these two days, it is said, gravitational forces balance out because the sun is directly over the equator. –H. Penny

A. Given a steady hand and the right egg– with little bumps that act as pods– you should be able to pull this off any day of the year, says Tel Aviv University astronomer and astrophysicist Noah Brosch. The position of the sun has nothing to do with it.

Factors such as egg shape, wind currents, floor vibrations, etc., would dwarf the sun's forces on the egg. Besides, if the equinox stuff were correct, you'd need to be located right on the equator.

If you have trouble egg-standing, try sprinkling salt on the table first, then gently blow away telltale grains around the base. The salt cubes act as tiny props.

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Send Strange questions to brothers Bill and Rich at strangetrue@cs.com.

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