Heat Transfer Demonstration Lab General Information

Heat can be thought of as a form of energy. It is in the near infrared on the electromagnetic spectrum. The ultimate source of most heat experienced on the Earth is from the sun. Much of the electromagnetic energy received from the sun is reflected, absorbed or scattered by the atmosphere before it reaches the Earth’s surface. Recall that the ionosphere absorbs much of the X-ray and ultraviolet energy. More of the ultraviolet energy reaching the Earth’s atmosphere is absorbed by the ozone layer in the stratosphere. In many cases, these forms of energy are converted from the shorter wavelength forms of ultraviolet and X-ray to the much longer wavelength form of infrared otherwise referred to as heat.

Recall as well that energy ALWAYS is transmitted from areas of high energy to areas of low energy. “Hot goes to Cold”. It is this principle that drives all weather systems on Earth. (And any other planet for that matter!)

Remember that heat is an expression of molecular motion. Atoms and molecules that have high rates of motion have high heat content.

There are three basic methods by which heat is transmitted from one area to another: conduction, convection and radiation.

Conduction is the direct transfer of heat energy from one substance to another.

As one high energy (“hot”) atom or molecule collides with another atom or molecule with less energy, some of the energy from the first is transferred to the second. In that way the second is “warmed up” and the first is “cooled off” this would continue until all molecules in the substance reached the same temperature. (Have the same heat content)

Different materials have different “abilities” to conduct heat. Generally, the more dense the substance, the better heat conductor it is, because the molecules are more closely packed and collisions between molecules occur more often. Water, air and soil are poor conductors of heat. Metals and rock are good conductors of heat.

Convection is the transfer of heat energy in a fluid (either liquid or gas)

Convection works on the principle that as a fluid is heated (molecules gain motion); the fluid expands and becomes less dense. A material that is less dense than the surrounding material will rise. In this way a heated fluid will transfer heat from one area to another.

For example, air over a landmass (which has absorbed heat and been warmed) will in turn absorb heat from the land and be warmed itself. As it is warmed it will rise, taking the heat with it. It will be replaced with cooler, denser air.

Radiation is the transfer of energy in the form of a wave

Radiation does not require the presence of matter to transfer energy. All of the energy we receive from the sun comes to us by this method.