Dr. Rosenberg wrote an article looking at the slipperiness of ice in the December issue of Physics Today, because he kept coming across the wrong explanation for it, one that dates back more than a century.

This explanation takes advantage of an unusual property of water: the solid form, ice, is less dense than the liquid form. That is why ice floats on water, while a cube of frozen alcohol  which has a freezing temperature of minus 173 degrees Fahrenheit  would plummet to the bottom of a glass of liquid alcohol. The lower density of ice also means that the melting temperature of ice can be lowered below the usual 32 degrees by squeezing on it.

According to the frequently cited  if incorrect  explanation of why ice is slippery under an ice skate, the pressure exerted along the blade lowers the melting temperature of the top layer of ice, the ice melts and the blade glides on a thin layer of water that refreezes to ice as soon as the blade passes.

"People will still say that when you ask them," Dr. Rosenberg said. "Textbooks are full of it."

But the explanation fails, he said, because the pressure-melting effect is small. A 150-pound person standing on ice wearing a pair of ice skates exerts a pressure of only 50 pounds per square inch on the ice. (A typical blade edge, which is not razor sharp, is about one-eighth of an inch wide and about 12 inches long, yielding a surface area of 1.5 square inches each or 3 square inches for two blades.) That amount of pressure lowers the melting temperature only a small amount, from 32 degrees to 31.97 degrees. Yet ice skaters can easily slip and fall at temperatures much colder.

The pressure-melting explanation also fails to explain why someone wearing flat-bottom shoes, with a much greater surface area that exerts even less pressure on the ice, can also slip on ice.