Physics and Technology – Physics – Thermodynamics
Warmth and cold are qualities that can be directly perceived by people. The physical principles underlying these phenomena long remained unclear and still remain difficult to understand.
Surprising connections between heat energy, statistics, and disorder are revealed by the basic laws of thermodynamics.
Physics and Technology – Physics – Heat and Temperature
Two objects combined behave like a body with the sum of both masses. However, if we pour cool water at 50°F (10°C) into warm water at 86°F (30°C), we obtain not 50°F + 86°F = 104°F (40°C), but water at 68°F (20°C).
The reason for this is that temperature and heat are phenomena of “many-particle” systems, or large assemblies of particles. They derive from the random movements carried out by all atoms or molecules in a substance. Named after their discoverer, the botanist Robert Brown (1773-1858), these vibrating, rotating, or lateral movements are called Brownian motion.
This motion can be modeled and predicted using the laws of stochastic processes and probability theory. In concrete terms, the temperature of a gas, for example, is the average random motion energy of the particles within it. A high temperature means that the particles are rapidly moving, vibrating, and rotating. Slower motion corresponds to lower temperatures.
Another term for temperature is “thermal energy” or “heat energy.” The term “heat” alone, on the other hand, de-scribes the energy that passes from one substance to another. For example, a carpeted floor feels “warmer” than a tile floor, since carpet drawsless heat energy out of our feet than ceramic tiles do at the same temperature.
Perpetual motion?
Even before people recognized what heat is, physicists were familiar with the so-called first law of thermo-dynamics. According to this law, the sum of mechanical work done and heat gained (or lost) remains constant. This is a direct consequence of the law of conservation of energy.
Anyone who is skeptical about it may try—like unsuccessful inventors of earlier generations—to build a perpetual motion machine, a closed system-based device that theoretically performs work without the addition of extra energy. The law of conservation of energy dooms these attempts to failure; however, that does not stop many people attempting to do it anyway.
The physical unit of temperature is the kelvin (not “kelvin degree”). Absolute zero lies at OK, while water freezes at273.15Kand boils at 373.15K. Yet most technical applications use the Celsius scale, in which water freezes at 0°C. On the Celsius scale, nominally negative temperatures can occur.
HEAT RADIATION
Every object constantly sends out electromagnetic radiation (p. 321), at frequencies and wavelengths that depend on its temperature. At room temperature, this heat radiation lies in
the infrared zone and is thus invisible to the human eye.
Snakes can perceive it, however, and it can be made visible using infrared cam- eras or night-vision devices. The heat radiation of objects at 5500 kelvin, on the other hand, is bright yellow visible light. This is the temperature of the sun’s surface.
ISSUES TO SOLVE
ASTRONOMERS have measured the prevailing temperature in space: 3K (-454°F). However, using special cooling devices—for instance, laser beams that slow atomic motion—scientists have reached even lower temperatures.
The record achieved by experimentation lies at less than a billionth of a kelvin. This may be the lowest temperature in the universe.