Conductors and Insulators

a. Transfer of Thermal Energy http://www.wiziq.com/tutorial/1316-Transfer-of-Thermal-Energy

b. Heat and Thermal Energy http://www.physics4kids.com/files/thermo_transfer.html

FILL IN THE BLANK

c. (Read "Thermal Insulation" to complete Part C

Thermal Insulation

by Ron Kurtus (revised 14 November 2014)

Thermal insulation is the method of inhibiting the transfer of thermal energy from one area to another. In other words, thermal insulation can keep an enclosed area such as a building warm, or it can keep the inside of a container cold.

Heat is transferred by from one material to another by conduction, convection and/or radiation. Insulators are used to minimize that transfer of heat energy. In home insulation, the R-value is an indication of how well a material insulates.

Questions you may have include:

Where is thermal insulation used?
How does insulation work?

This lesson will answer those questions. Useful tool: Units Conversion

Where thermal insulation is used

If you have an object or area that is at a certain temperature, you may want to prevent that material from becoming the same temperature as neighboring materials. This is usually done by employing a thermal insulation barrier.

For example:

If the air outside is cold, you may want to protect your skin by wearing clothes that keep the cold out and the body warmth in.
If your house has cool air inside during the summer, you may want to prevent the temperature from becoming the same as the hot air outside by having the house well insulated.
If you have a hot drink, you may want to prevent it from becoming room temperature by putting it in a thermos bottle.

In any location where there are materials of two drastically different temperatures, you may want to provide an insulating barrier to prevent one from becoming the same temperature as the other. In such situations, the effort is to minimize the transfer of heat from one area to another.

How insulation works

Insulation is a barrier that minimizes the transfer of heat energy from one material to another by reducing the conduction, convection and/or radiation effects.

Insulating materials

Most insulation is used to prevent the conduction of heat. In some cases radiation is a factor. A good insulator is obviously a poor conductor.

Less dense materials are better insulators. The denser the material, the closer its atoms are together. That means the transfer of energy of one atom to the next is more effective. Thus, gases insulate better than liquids, which in turn insulate better than solids.

An interesting fact is that poor conductors of electricity are also poor heat conductors. Wood is a much better insulator than copper. The reason is that metals that conduct electricity allow free electrons to roam through the material. This enhances the transfer of energy from one area to another in the metal. Without this ability, the material--like wood--does not conduct heat well.

Insulation from conduction

Conduction occurs when materials—especially solids—are in direct contact with each other. High kinetic energy atoms and molecules bump into their neighbors, increasing the neighbor's energy. This increase in energy can flow through materials and from one material to another.

Solid to solid

To slow down the transfer of heat by conduction from one solid to another, materials that are poor conductors are placed in between the solids. Examples include:

Fiberglass is not a good conductor nor is air. That is why bundles of loosely packed fiberglass strands are often used as insulation between the outer and inner walls of a house.
Conductive heat cannot travel though a vacuum. That is why a thermos bottle has an evacuated lining. This type of heat cannot be transferred from one layer to the other through the thermos bottle vacuum.

Gas to solid

To slow down the heat transfer between air and a solid, a poor conductor of heat is placed in between.

A good example of this is placing a layer of clothing between you and the cold outside air in the winter. If the cold air was in contact with your skin, it would lower the skin's temperature. The clothing slows down that heat loss. Also, the clothing prevents body heat from leaving and being lost to the cold air.

Liquid to solid

Likewise, when you swim in water, cold water can lower your body temperature through conduction. That is why some swimmers wear rubber wet suits to insulate them from the cold water.

Insulation from convection

Convection is transfer of heat when a fluid is in motion. Since air and water do not readily conduct heat, they often transfer heat (or cold) through their motion. A fan-driven furnace is an example of this.

Insulation from heat transfer by convection is usually done by either preventing the motion of the fluid or protecting from the convection. Wearing protective clothing on a cold, windy day will inhibit the loss of heat due to convection.

Insulation from radiation

Hot and even warm objects radiate infra-red electromagnetic waves, which can heat up objects at a distance, as well as lose energy themselves. Insulation against heat transfer by radiation is usually done by using reflective materials.

A thermos bottle not only has an evacuated lining to prevent heat transfer by conduction, but it also is made of shiny material to prevent radiation heat transfer. Radiation from warm food inside the thermos bottle is reflected back to itself. Radiation from warm outside material is reflected to prevent heating cold liquids inside the bottle.

Part D.

Challenge Question:

https://ca.pbslearningmedia.org/resource/lsps07-sci-phys-thermalenergy/thermal-energy-transfer/#.Wox94BPwZsM

What is this best way to insulate your house?

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