# Warm-Up Exercise for lecture 21

## Due 8:00 am, Tues, Nov 11

Physics 105, Fall 2008

Which is coldest?
0 degrees Centigrade (Celsius)
0 degrees Kelvin
0 degrees Fahrenheit

Suppose we have two jars of gas: one of helium and one of neon. If both jars have the same volume, and the two gases are at the same pressure and temperature, which jar contains the greatest number of gas molecules? (For this question and the next, consider both gases to obey the ideal gas law. Also note that the mass of a neon molecule is greater than the mass of a helium molecule.)
jar of helium
jar of neon
same number.

You mix some helium and neon gas together in the same container so they are at the same temperature. The average kinetic energy per helium molecule is
greater than
less than
equal to
the average kinetic energy per neon molecule.

Ralph has a question about the reading assignment. The book says that if we heat up a metal washer, all dimensions of the washer increase, including the diameter of the hole. That is, the hole itself gets larger! It seems to Ralph that the expansion of the metal would cause the outer diameter to increase but the hole to decrease, because the metal expands into the hole. Can you help Ralph understand how/why the hole gets larger?