Basic scientific principles for reference

Posted Wednesday, July 31, 2013 in Sustainable Maine

Basic scientific principles for reference

by Paul Kando

From time to time I find it useful to brush up on my scientific literacy. Maybe you do too. Since many scientific principles appear in these columns, I've been asked by many readers to explain some of them in depth.  Here is some of the basic science to which these columns routinely refer:

Thermodynamics and energy

According to the First Law of Thermodynamics, energy can neither be created nor destroyed, but it can be converted to various forms (chemical, electric, thermal, kinetic, magnetic, nuclear, ionizing, gravitational).  Energy is the capacity to do work (heat water, lift weight, move an object, emit sound, etc.), subject to the Second Law of Thermodynamics: in a closed system, the capacity of energy to do work decreases. This deterioration is called entropy --  in a closed system entropy increases. Your warm house cools. You must add more energy from the outside to keep it warm.

Except for geothermal processes which only rarely affect the surface, Earth’s sole energy source is the ongoing nuclear fusion in the Sun. As two radioactive Hydrogen isotopes, Deuterium (1H) and Tritium (2H) fuse into Helium (He), a neutron and lots of energy are released. The amount can be calculated using Einstein’s famous equation e=mc2, where e=energy, m=mass and c is the electromagnetic constant, a.k.a. the speed of light (299,792,458 meters per second – close enough to remember as 300,000 km/sec. or 186,000 miles/sec.)

Energy and temperature

As matter (air, water, objects on Earth) absorb the Sun’s electromagnetic radiation (of various wavelengths/frequencies, including visible light), its molecular vibration intensifies. (The radiated energy performs work, converts to heat, its entropy increases). Temperature is a measure of molecular vibration. The Kelvin (K), Celsius (ºC) and Fahrenheit (ºF) scales are calibrated using the phase changes of water –solid to liquid to vapor – as  reference. A K is identical  to a ºC, but 0ºC marks the freezing point of water and 0 K marks “absolute zero”, the lowest possible temperature where no heat energy remains in a substance. Water freezes at 0ºC, 273.15 K and 32ºF; boils at 100ºC, 373.15 K and 212ºF. (Of course  0 K = –273.15ºC).

Heat

Heat flows from any object at a different temperature from its surroundings, until the object and the surroundings reach the same temperature, i.e. thermal equilibrium. Heat always flows from the higher temperature to the lower, consistent with the second law of thermodynamics.  In general, the universe seeks equilibrium. Pressure, the absence of equilibrium, causes flow. (A pump increases or decreases pressure).

Heat flows by radiation, conduction or convection. Radiation requires no material intermediary (sunlight radiates through space). Conduction requires a conductor (a metal spoon left in a boiling pot of soup).  Convection is heat absorbed by a flowing fluid (e.g. water or air) as explained below. You can’t make heat move in the opposite direction, but you can add energy: a boiler warms circulating water to a higher temperature than a heated room; a heat pump’s compressor boosts the temperature of a refrigerant, adding heat-energy by increasing pressure.

Conditions of life on Earth and comfort in a house both depend on the interactions of heat, air and water. Heated air expands, becomes lighter by volume, and rises. As it warms, air absorbs more and more moisture in the form of water vapor (relative humidity). When frozen water absorbs heat, it melts, when fluid water warms, it evaporates. The vapor is absorbed by warming air and rises with it. The rising air and vapor contain the heat they have absorbed: this is convection. When the warm air cools, it releases the water vapor it can no longer hold and the vapor condenses into liquid. (it rains; moisture precipitates on the underside of your cold roof).  As air and moisture cool, they release the energy they absorbed when warming. In moisture this is significant: it takes extra energy to produce a phase change: 1 Btu of energy heats 1 lb of water by 1ºF, but 144 Btus melts 1 lb of ice (heat of fusion), and 970 Btus evaporates 1 lb. of water (heat of evaporation). According to the laws of thermodynamics, energy absorbed by heating air and water cannot be lost: This is the energy that intensifies a storm even as its rains inundate the land.  If warm, moist air flows into your attic through air leaks, the energy it took to vaporize your shower water, for example, may heat your snowy roof and cause an ice-dam.

Cycles of nature

Life on Earth is possible because of the balance nature maintains. Plants use solar energy to make carbohydrates from water and carbon dioxide, exhaling oxygen.  Animals inhale oxygen and exhale carbon dioxide. Greenhouse gases keep the planet livable. All living matter is continually recycled through cycles of birth, growth, death and rebirth. Processes of fermentation and decay produce methane and, eventually, hydrocarbon fossils -- millions of years’ worth of solar energy stored up by living things. Burning millions of years’ worth of stored energy and releasing excess greenhouse gases destroys nature’s life-sustaining balance – threatening life itself.  

These are the basics. The rest is mostly detail. People ignorant of the basics have a harder time seeing how the world works. They often fall prey to myth-makers and propagandists whose bread and butter is to obfuscate about detail. Climate change deniers, for example, endlessly question details like short term variations in air and sea temperature, local weather patterns, this year’s extent of polar or glacier ice, and so on. They detest true science, but know better than to question the laws of thermodynamics or whether water evaporates when heated.   

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