A key to understanding environmental process is to understand the ways in which energy can flow or move through a system. Remember that change can occur only if energy is involved in some form of transfer or transformation. So it is important to determine if there are rules that control these energy changes.

The laws of thermodynamics are statements about these rules. You already know that the amount of energy in the universe is fixed and that useful energy is always "lost" when work is done or change occurs. Another way to state the second law is that energy always flows from a state of high energy to one of low energy or in less general terms heat always flows from hot to cold. This means that heat never leaves a refrigerator unless work is being done to remove the heat. To make a cold thing colder and a hot thing hotter is to decrease entropy because energy is being ordered or sequestered into a small portion of the universe. It also means that if there is a situation where some area is hot and another is cold, heat naturally flows from the hot area to the cold and may, and I emphasize the word may, cause changes to occur as that heat is transferred.

Convection occurs when a material that is able to flow is hot in one area and cool in another. Because hot matter is less dense than cold -- heated molecules move further apart, the hot less dense areas tend to rise while cooler, denser material sinks. To go back to the stove, heat some water and pour it into a glass coffee cup. Place an ice cube in the water and add a drop of food coloring. You will be able to see the blue dye carried down by a cold current and then back to the surface as the cold water is heated by its surroundings. In the earth, convection currents are usually a much faster form of heat transfer than conduction with currents moving at 5 to 10 cm per year in the earth's rock interior and at upwards of 200 km/hr in the atmosphere. And, because convection currents are moving matter, they have the potential do work. Volcanoes, earthquakes, hurricanes and tornadoes are caused by convection.

Radiation is the third method of heat transfer. It becomes important process when hotter matter is "visible" to colder, for example, the radiation of heat from the earth's surface to space. Because earth's surface at an average of about 25° C can "see" cold outer space, the surface releases energy in the form of infra-red radiation. Some of this is trapped by the atmosphere and warms the air, but the large bulk of the radiation passes into space and is lost to the earth. As a result the earth surface is constantly losing energy and would already be a very cold place if it were not also constantly being heated by radiant energy from the sun. Radiative transfer is by far the fastest method of heat transfer since radiation moves at the speed of light -- 300,000 km/sec. You can experience this difference in rate of action at the shore on a summer day. The surface of the sand heated by radiant energy of the sun gets very hot, but just below the surface, the sand remains cool. (Why do you think the surface of the ocean doesn't get as hot as the sand?

Reading question: Give examples of how you might experience radiation, conduction, and convection in the vicinity of an incandescent light bulb.

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