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Heat transfer is the exchange of heat by conduction, convection, or radiation within a substance, or between a substance and its surroundings.
Conduction is the transfer of thermal energy by molecular or electronic collision within a substance. The flooring at work is a perfect example of conduction. The carpet feels warmer than the linoleum when I step on it, because the linoleum is a faster conductor of the thermal energy in my foot.
Convection is the transfer of thermal energy in a gas or liquid by means of currents in the heated fluid. The fluid flows and carries energy with it. An example of this would be the boiling water above. As the thermal energy comes through the pan, it heats the water, and the energy is scattered through the water by the waves.
Newton's law of cooling is also demonstrated in this transfer of thermal energy. According to Newton, the rate of cooling is proportional to the temperature difference between the object and its surroundings. Since the ice cube has a lower temperature, the pan will warm it. This will cause the molecules to vibrate more, until it actually melts the ice cube.
Radiation is energy that is transmitted in the form of rays or waves or particles. A microwave uses radiation to transfer thermal energy to food to cook it or warm it. Radiation can also be seen in the form of electromagnetic waves, like radio towers, infrared waves, and light waves.
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| (solid) |
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| (solid turning to liquid) |
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| (liquid turning to gas) |
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| (gas turning into a liquid) |
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| (liquid turning to solid) |
The ice cube sitting in the heated pan will melt because the heat transfers from the pan onto the ice cube (solid). The ice cube is given enough energy to melt into water (liquid). As more energy passes from the pan to the water, the water will heat up enough to boil, turning the water into a gas. If enough energy was added to the gas, it could be changed into plasma. The process can work the other way around, as well. Plasma can become gas. Gas can turn into liquid (condensation). Liquid can become a solid by freezing.
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