STRANGE BUT TRUE- Blow out: Don't burp while lighting up


Q. Well, excuse us, but when might stomach or intestinal gas have explosive consequences? –J. Carrey

A. Forget those flame-throwing flatulators of college campuses of the 1960s. For this one, you can just ask your doctor: surgical teams must take precautions to ensure that fires and explosions do not occur near or within a patient, since some 40 percent of the gas in the large intestine may be hydrogen and methane, says Jearl Walker in The Flying Circus of Physics. Procedures such as removal of polyps require extreme care. Any heating or sparking during electrical cauterization can cause the gases to blow up, burning and rupturing the intestines. 

During one colonoscopy, there was a loud explosion, and a blue flame shot out of the colonoscope for about a meter. Current protocol calls for the patient to fast for up to a day so that the intestines are empty. (Surgical fires today are rare, estimated at less than 1 in a million.)

Flammable gases can also be produced in the stomach when it doesn't empty properly. In one case, a man lit a cigarette just as he belched uncontrollably: the cigarette shot from his mouth like a rocket, and his lips and fingers were burned. In another, when a guy lighting a cigarette belched, "the gas came up through his nostrils with a flare shooting out of each, making him look like a medieval, fire- breathing dragon." 

Q. No point asking a scorpion about the math involved, but it sure knows how to apply some in hunting down a beetle. Explain.–J. Wayne

A. The moving beetle inadvertently sends two sets of pulses along the sand's surface, one in the form of longitudinal waves that oscillate forward and backward at 150 meters per second (m/s), another in the form of transverse waves that go side to side at 50 m/s, says David Halliday in Fundamentals of Physics. 

That's a big difference, apparently detectable by the scorpion, which is nocturnal and can neither see nor hear the beetle. What the scorpion does is stand with its eight legs roughly in a circle so that now the faster pulses are felt first, then the slower ones. The direction to the beetle is given by the first leg to feel a vibration; the distance is given by the time interval between the arrival of the two pulses. Having mastered the mental math (distance = 75 m/s x the time lapse), the predator scorpion turns toward the beetle and mad-dashes for dinner.

Q. "Stay on the ice and pay the price" runs the old hockey adage. Who's paying what and why? –J. Frost  

A. For this fast-paced game, exhaustion is often a problem at the uncoached amateur level, as some players hog the ice time even to the point where a good player can be outpaced by a mediocre defenseman, says Alain Hache in The Physics of Hockey. Hockey's energy drain is greater than other team sports like basketball and baseball, with National Hockey League players skating at speeds in excess of 25 mph (40 km/hr). The legendary Bobby Hull, fastest of his time, was once clocked at 29.2 mph (47 km/h), and after he had spent 29 minutes on the ice during one game, sports scientists figured he had skated a total of about 8 miles (13 kms). So it's not surprising that during 60 minutes of regulation time, a player can burn several hundred calories and lose up to 10 pounds.

Typically, players hold their speed at about 75 percent of maximum, budgeting their energies as they wait to see how play will evolve. "We can now understand why NHL athletes take many short shifts on the ice (usually less than a minute each) rather than fewer long ones," says Hache. "This is the best way to operate at optimal capacity."   

Q. Why are there five spikes on stars on the American flag, six on the Jewish Star of David? That's certainly not what you see in the sky on a starry night. Or is it? –B. Ross

A. It's true, real stars have no spikes but are almost perfect spheres which from a distance should appear as tiny dots, says Indiana University vision scientist Arthur Bradley. Corneal scratches are not the cause of the spikes, as some have asserted, but imperfect eye-optics is.

Probably it has something to do with the lenses of the eyes, which sit right behind the corneas. Since these grow and change throughout life, "It turns out that individuals have their own characteristic star-imperfections that change with age." Thus, you're seeing your own private spiky "Starry Night," though not apt to rival van Gogh's.

On a clear night, poke a small (2 mm) hole in a piece of dark card and look at a star. Move the card around, and you will make the spikes appear and disappear. 

"Basically, the card blocks light from passing through the part of the eye optics that generates the spikes," says Bradley. "Try it, and you'll see for yourself."

Send Strange questions to brothers Bill and Rich at