Chapter 3
Heat and Making Things Cold

Is there a difference between temperature and heat? Temperature is a measurement of how hot and cold something is, but heat is energy. Energy is created when molecules have motion. It does not matter what state of matter something is in for the atoms to stop moving. Atoms have more atom motion in gas than liquid, and liquid has more atom motion than a solid does.

Making Things Cold
One way of cooling things is by evaporation. The change from the liquid state to gaseous state can make things cold.

Liquid cools because some molecules have more energy than others. The atoms with more energy are more likely to become gas. The less energetic ones are left behind now. This is the reason why liquid cools.

Another way to cool is by gas escaping and expanding. This happens because atoms are in patterns, with solids in tighter patterns, and gas in less tight patterns. When the gas expands the atoms move farther away from each other, and as the atoms slow down the gas cools.

The Throttling Process and Joule-Thompson Effect
The throttling process is a method of cooling, based on expansion, in which liquid or gas in a high pressure area seep into a region that has low pressure. This results in cooling.

Joule and Thompson (commonly known as Lord Kelvin) constructed an experiment in which they kept gas in a region at a constant temperature, and let the gas seep through a porous plug of cotton into an area of lower pressure. As the gas expanded it became cooler. This is known as the Joule-Thompson Effect.

Helium
Heike Kamerlingh Onnes, at the University of Leiden in the Netherlands, liquefied helium in July 1908. He was awarded the Nobel Prize in physics in 1913. Helium was important in the topic of superconductivity because superconductors lose all resistance at very cold temperatures. Liquid helium can be achieved at the temperature as low as 0.7K.

"Superconductivity is perhaps the most remarkable physical property in the universe"
- David Pines, University of Illinois Urbana-Champaign Center for Advanced Study Professor of physics and electrical and computing engineering