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Wisconsin Department of Natural Resources

Why Is Ice Slippery?

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Wisconsin Department of Natural Resources

If you’ve ever shakily stepped onto the ice at your local skating rink, you are intimately familiar with the fear of falling on slippery ice. But what makes ice so slippery in the first place? Interestingly enough, scientists are still trying to figure that one out.

Physicists used to believe that ice became slippery when it was exposed to applied pressure. This pressure, they theorized, lowered the melting temperature of the top layer of ice. They believed that when a person went ice skating, the pressure from the blade caused the topmost layer of ice to melt. The thin layer of water allowed the ice skate to glide easily over the surface. After the blade passed, the top layer of water refroze.

However, most scientists today claim that this theory is wrong. “Ice is a very mysterious solid,” Robert M. Rosenberg, a chemistry professor at Lawrence University, said in an interview with The New York Times.

Scientists found that while pressure does lower the melting point of ice, it only does so by a fraction of a degree. Instead, they proposed that the friction from an ice skate causes the ice to melt beneath it.

Others believe that ice naturally possesses a fluid layer comprised of unstable water molecules. While these molecules search for stability, they move chaotically over the ice’s surface and create a slippery layer.

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Big Questions
Why Does Having a Fever Make You Feel Cold?
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During fever, why do we feel cold when our body temperature rises?

Nicole Van Groningen:

Anyone who has ever had the flu knows that fever isn’t uncomfortable because you feel hot—it’s uncomfortable because you feel freezing cold. You get goosebumps, you’re shivering, you’re piling on the covers.

Fever, also known as pyrexia, is defined as an elevation in body temperature above the normal range due to an increase in the body’s natural set point. Most people associate fever with infections, but fever can also frequently occur with autoimmune diseases, cancer, drug reactions, and even blood clots. Fever is not a direct result of these conditions, but rather a consequence of triggering the body’s inflammatory pathways. One key member of this inflammatory cascade is a group of molecules called pyrogens, which directly interact with the hypothalamus in the brain to produce fever.

The hypothalamus serves as the body’s thermostat. When triggered by pyrogens, the hypothalamus tells the body to generate heat by inducing shivering, goosebumps, and constriction of blood vessels near the surface of the skin. It even causes a subjective feeling of cold, which encourages behavioral responses to raise the body temperature, like reaching for the covers.

All of these things are adaptive when your body temperature falls below its usual set-point (about 98.6 degrees Fahrenheit), which typically occurs in cold weather. But they become abnormal in the setting of fever, when your hypothalamus signals to the body to raise its temperature well above the normal range.

If pyrogens suddenly disappear from the bloodstream, as is the case with intermittent fevers, the hypothalamus all of a sudden senses that things are way too hot, and tells the body to kick in its usual cooling-off mechanisms. That’s why people sweat profusely when their fever “breaks.”

This post originally appeared on Quora. Click here to view.

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Big Questions
Why Do We Sing the National Anthem at Sporting Events?
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Rich Schultz/Getty Images

In early September 1814, Francis Scott Key, an American lawyer and amateur poet, accompanied American Prisoner Exchange Agent Colonel John Stuart Skinner to negotiate a prisoner release with several officers of the British Navy. During the negotiations, Key and Skinner learned of the British intention to attack the city of Baltimore, as well as the strength and positions of British forces. They were not permitted to leave for the duration of the battle and witnessed the bombardment of Baltimore's Fort McHenry on September 13 and 14. Inspired by the American victory and the sight of the American flag flying high in the morning, Key wrote a poem titled "The Defence of Fort McHenry."

Key set the lyrics to the anthem of the London-based Anacreontic Society, "The Anacreontic Song." (Nine years earlier, Key had used the same tune for “When the Warrior Returns (from the Battle Afar)” to celebrate Stephen Decatur’s return from fighting the Barbary pirates, which included the line “By the light of the Star Spangled flag of our nation.”)

The poem was taken to a printer, who made broadside copies of it. A few days later, the Baltimore Patriot and The Baltimore American printed the poem with the note "Tune: Anacreon in Heaven." Later, Carrs Music Store in Baltimore published the words and music together as "The Star Spangled Banner."

The song gained popularity over the course of the 19th century and was often played at public events like parades and Independence Day celebrations (and, on occasion, sporting events). In 1889, the Secretary of the Navy ordered it the official tune to be played during the raising of the flag. In 1916, President Woodrow Wilson ordered that it be played at all military ceremonies and other appropriate occasions, making it something of an unofficial national anthem.

After America's entrance into World War I, Major League Baseball games often featured patriotic rituals, such as players marching in formation during pregame military drills and bands playing patriotic songs. During the seventh-inning stretch of Game One of the 1918 World Series, the band erupted into "The Star-Spangled Banner." The Cubs and Red Sox players faced the centerfield flag pole and stood at attention. The crowd, already on their feet, began to sing along and applauded at the end of the song.

Given the positive reaction, the band played the song during the next two games, and when the Series moved to Boston, the Red Sox owner brought in a band and had the song played before the start of each remaining contest. After the war (and after the song was made the national anthem in 1931), the song continued to be played at baseball games, but only on special occasions like opening day, national holidays, and World Series games.

During World War II, baseball games again became venues for large-scale displays of patriotism, and technological advances in public address systems allowed songs to be played without a band. "The Star-Spangled Banner" was played before games throughout the course of the war, and by the time the war was over, the pregame singing of the national anthem had become cemented as a baseball ritual, after which it spread to other sports.

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