|MadSci Network: Physics|
Hi Chelsea, This is a question that might be better answered by a geologist or a soil engineer; however, I will talk about the physics involved in soil heat loss. Thermal conductivity and heat capacity are two things, which effect heat loss. Thermal conductivity is a measure of how fast heat flows through an object. Thermal energy (heat) causes atoms and molecules to move or vibrate. The more heat, the faster the vibration. When a hot vibrating atom comes into contact with another colder atom it transfers some of is energy to the colder atom. After the collision, the hot atom moves slower and the colder atom moves faster. Packing things closer together (increasing the density) increases the number of collisions between atoms and improves the thermal conductivity. Moving things farther apart decreases the number of collisions and reduces the thermal conductivity. In terms of soils, sand has a lot of space between grains (lower density). Sand should be a poorer conductor of heat than clay, which is denser. How tightly compacted the soil is will also effect the transfer of heat. Loose soils tend to be better insulators (lower thermal conductivity) than tightly compacted soils. Heat capacity is the ability to store energy. Heat capacity is also related to the density. Each vibrating atom is storing energy. A higher density material has more atoms in a given volume. More vibrating atoms store more energy. Water has a high heat capacity and is often used to store thermal energy. Wet sand can store more energy than dry sand. The water molecules fill the space between the grains of sand increasing the density of the sand. The higher energy content means that it will take longer to cool down. The higher density of wet sand also means that it can conduct heat faster than dry sand. The water content of a soil thus has a large effect on how much energy is stored and how fast it is lost. For more information try using the words soil engineer or soil engineering in your web search. I found a lot of references, which I think you will find usefull. The web is a wonderful place to find information. Congratulations on finding madsci.org and good luck with that soil research project. Bob Novak
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