'Rifling' a football helps the pass receiver catch it

Question: In American football, why does the quarterback generally try to "rifle" the ball to the pass receiver?

Answer: "Rifling" is a firearm's term that refers to the spiral grooves along the bore's interior to impart spin to the bullet, says Jearl Walker in "The Flying Circus of Physics."

The quarterback tries to do the same with the football, which acts like a gyroscope in maintaining its orientation and flying smoothly instead of tumbling. Now the ball will travel farther, and with strong enough spin, will gradually "nose down" as its passes through its arced trajectory, making it easier for the receiver to make the catch.

Failure to spin the ball properly could result in a wobbly pass — or even an end-over-end "duck" — shorter and trickier to grab hold of. When a punter (kicker) puts spin on the ball, usually the intent is to get it to travel farther and also to increase "hang time" so the punter's team can get down field before the ball comes down.

As for the spinning bullet, if one is aimed directly upward it will sometimes maintain its stability throughout the flight, returning base first to the ground. Although probably not lethal, the bullet could still injure someone. If it tumbles while falling, it will come in much slower than its muzzle speed, lessening the chance of injury. "Still, if someone near you starts shooting in the air, you best hide instead of standing in the open in admiration."

Question: You might think boiling an egg would be pretty much standard around the world. Think again.

Answer: The science of high-altitude cooking is well known to residents of more mountainous regions like Colorado where atmospheric pressure affects water-boiling temperature, says Goran Grimvall in "Brainteaser Physics."

Try to boil eggs atop Mount Everest (29,000 ft.), where water boils at about 72 degrees C (162 F) instead of 100 C (212 F) at sea level, and you better keep a book handy. Egg proteins change their structure at about 63-66 C, first in the whites, then in the yolk. Even at 85 C (185 F), it takes half an hour to get a 3-minute egg.

That's a plenty big factor, based on about 160 millibars atmospheric pressure difference from, say, New York to Denver. By comparison, the difference between a low-pressure stormy day and a high-pressure day is less than about 50 millibars, so you don't need to check the weather before setting the egg-timer.