QUESTION: Many balls used in sports are pressurized. Some balls have valve stems for pressurizing. How are balls such as tennis balls pressurized? (Asked by a curious tennis player.)

REPLY: This question reminds me of the one about how they get lead in pencils. I answered that one once – remember, the pencil wood is in two pieces, which are put together after the lead is placed between them during manufacture.

The explanation for pressurizing tennis balls is similar. They are pressurized during manufacture. On a racquetball, there is a visible seam and the ball is pressurized before it is sealed. You don’t see this seam on a tennis ball, which has a pressurized rubber core covered with cloth, usually wool mixed with up to 35 percent nylon. Tennis balls gradually lose their pressure or go “soft” with use. You might have noticed the frequent change of balls in tournament play. To be a good one, a ball must bounce between 53 and 58 inches high when dropped from a height of 100 inches onto a concrete surface. (Now you know how to test your tennis balls.)

There are different types of tennis balls for different conditions. The “regular” ball is used on clay and indoor courts. The grass court ball has a treated felt covering for grass court surfaces. The extra-duty ball has heavy-duty felt for hard, abrasive outdoor courts. And, there is a high-altitude ball for all courts at altitudes above 3,500 feet. (Balls with regular pressurization would get more bounce in Denver -- the mile-high city.)

QUESTION: Why is crossing the street in the wrong place called jaywalking? (Asked by a curious column-reader.)

REPLY: According to what I read, there were a lot of blue jays along the east coast during colonial times. As the population grew, the blue jays headed for the countryside, and “jay” became an expression for a “hick” or country bumpkin.

Rural folk coming to the big cities often crossed in the middle of the street, rather than at an intersection. This was referred to as “jaywalking” or “hick walking.”

Another term applied to us rural folk (I was raised in the country) is “hillbilly” -- not even a formal hillwilliam. The “hill” part is easy to understand. The “billy” means “guy” or a general name for a male, such as Mac (hey Mac). Another example is a billy goat -- a male goat. So, hillbilly meant a guy from the hills -- not a goat from the hills.

C.P.S. (Curious Postscript): “Duct tape is like the Force; it has a dark side, a light side, and it’s what holds the universe together.” --Anonymous

Curious about something? Send your questions to Dr. Jerry D. Wilson, College of Science and Mathematics, Lander University, Greenwood, SC 29649, or e-mail jerry@curiosity-corner.net. Selected questions will appear in the Curiosity Corner. For Curiosity Corner background, go to curiosity-corner.net.