Filed under:

Strange but true: Uneven friction gives stone its curl

Q: In the popular winter Olympic sport of curling — think shuffleboard on ice, with four members on a team — a 42-pound banded stone is sent sliding over an ice rink toward a target region. The stone starts out going straight but curves gradually to one side, increasing near the end.

What's the point of this "curl," and how is it done?

A: Skilled curlers use it to finesse their stone around other stones that might shield the target, says Jearl Walker in "The Flying Circus of Physics."

This sideways deflection comes from the friction between the stone's narrow circular band and a thin layer of liquid water melted from the ice.

Due to the stone's spin, the speed of the band varies from point to point, causing variable friction and deflecting the stone. This uneven friction also accounts for the stone's behavior at the end of its glide, spinning around one side as if pinned there. Curling is often played on pebbled ice (with small upward protrusions), possibly to exaggerate the deflection.

Vigorous sweeping of the ice just in front of the stone (a colorful feature for spectators) is thought by many players to add length to the path and to increase the curl. "While the sweeping is sometimes unfairly scoffed at, it certainly removes grit and loose ice that would hinder the stone, but it may also lubricate the stone's motion by partially melting the ice."

Q: When a domestic cat leaves home and stays away for days at a time, where does it go? What new techno-tool might tell the "tail"?

A: That was the puzzle for cat companion and "tinkerer by temperament" Mark Spezio, who rigged up his beloved KooKoo's collar with an inexpensive, lightweight GPS logger before setting him loose, says "IEEE Spectrum" magazine.

When KooKoo returned from an 11-hour stretch, Spezio downloaded the GPS data to his computer to map out the cat's wanderings: He had traveled about 5 miles, taking in neighborhood yards and rooftop hangouts, plus his favorite — a storm water basin area with plenty of trees and tall grass and birds, mice and other rodents. Little wonder this is where KooKoo had spent 80 percent of his time. Still concerned about these long absences, Spezio started searching out KooKoo at the basin area. Luckily, there's a happy ending for the tale of the GPS-enabled cat, who subsequently began spending far fewer worrisome nights away from home.

Q: About 7 billion of us humans are alive today, twice as many as in 1965, with roughly 75 million added every year. By U.N. predictions, there could be another 2 billion to 4 billion by 2050. But growth hasn't occurred every day. Can you cite a few of those extremely rare days when world population actually shrank?

A: The most recent was Dec. 26, 2004, when the Indian Ocean tsunami killed nearly 250,000 people, says Alison George in "New Scientist" magazine.

Another 160,000 died of other causes, and the day's 370,000 births couldn't compensate, reports environmentalist Robert Engelman in his book "More."

Other such days include the Tangshan earthquake in China on July 28, 1976, and the devastating cyclone that hit Bangladesh on Nov. 12, 1970, each killing 250,000; and also the 70,000 deaths caused by the atomic bomb on Hiroshima, Japan, on Aug. 6, 1945. Historically, the flu pandemic of 1918-1920 at about 50 million deaths almost certainly stalled the world's upward population trend.

The biggest "hit" was the Black Death of the 14th century at perhaps 75 million, reducing Europe's population by 30 percent. "Things will be very different in the future," says George.

"There will still be disasters and wars, of course, but sometime after 2050, the world will enter a new era when the population will shrink on many days. We will simply be having fewer children."

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