Heat Transfer
Heat is a form of kinetic energy, a measurement of the vibrations in all of the molecules around you. In a solid object, the atoms vibrate but hold their shape. In a liquid, they can move around, but must hold the same volume. In a gas, they can move freely, and the gas can expand or contract. We usually think of temperature when we think of heat. Temperature is a measure of the average kinetic energy of an object, while heat itself is the total kinetic energy of an object. From another site describing heat transfer, "Did you know that there is more heat in an iceberg than a pot of boiling water? The pot of water actually has a higher temperature, but the iceberg is much bigger; and therefore, contains far more molecules (though they move at a much slower rate) [and greater total heat energy]."
Heat can be transferred in three ways (learn more here). First, through conduction, one atom which is vibrating bounces off of another, causing it to start vibrating. This typically only has a significant effect in solids. Heat is directly transfered from atom to atom.
The second method is through convection. This is where fluids, like liquids and gases, move around and their kinetic energy moves with them. It is by the movement of the fluid that the heat energy is carried to a different place.
The final way for heat to move is through radiation. This is the only type of heat transfer that can move through a vacuum, and therefore must be how we are heated by the sun. Energy at certain specific wavelengths, typically infrared, can carry heat energy. Many people say that on a hot day, if you wear a brightly colored shirt, you will not be as hot, because a darker shirt would absorb more energy from the sun.
Heat capacity is a measurement of how much energy it takes to heat a particular substance. For water, it is 4.184 joules needed to raise 1 gram of water exactly 1 degree Celcius. That is actually a lot of energy, especially when you compare it with other substances, like gold. Gold's heat capacity is 0.129 joules needed to raise one gram one degree Celcius. Although the number is lower, it means that if you add the same amount of energy to an equal amount of gold and water, the gold will have a much higher jump in temperature. An example is when you are boiling water on a stove, the water takes a while to heat, although the metal container heats very quickly. The heated metal quickly spreads the heat over more of the surface of the water, helping the water heat more quickly.
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Nuclear Power, and most other forms of power, produce electricity by moving heat into steam molecules, causing them to turn a turbine. Understanding how heat is transferred is crucial to understanding how electricity is produced.
Fundamental Forces, especially electromagnetic forces, cause the heat capacity of water to be very high. Water has a property called the hydrogen bond, caused by electromagnetic attractions between different parts of the water molecule. These forces have a drastic effect on causing water's heat capacity to be so high.
Sea-floor Spreading is caused by the convection of hot chunks of magma to the surface. Because the core of the Earth is so hot, the magma is pushed to the surface and causes the sea floor to spread in certain places.
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© 2008 Michael F. Robbins
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