Atmospheric Processes — Conduction

In this activity, students will explore the process of conduction. A classroom demonstration is included to further student understanding of the process.

Background

Conduction is one of the ways that energy is transferred from the earth's atmosphere to the air. Conduction is the process by which heat energy is transmitted through collisions between neighboring molecules.

Think of a frying pan set over an open camp stove. The fire's heat causes molecules in the pan to vibrate faster, making it hotter. These vibrating molecules collide with their neighboring molecules, making them also vibrate faster. This process continues until the entire pan has heated up due to the vibrating and colliding molecules. If you've ever touched the metal handle of a hot pan without a potholder, you have first-hand experience with heat conduction!

Some solids, such as metals, are good heat conductors, while others, such as wood, are poor conductors. Air and water are relatively poor conductors and thus are called insulators. Not surprisingly, many pots and pans have insulated handles.

What does conduction have to do with the atmosphere? Air is a poor conductor of heat energy but a good insulator. Imagine that you're a mountaineer, climbing Mt. Everest. Near the summit, you'll probably be wearing a thick down jacket and pants to guard against the extreme cold. It's not the down itself that keeps you warm. Rather, it's the enormous number of tiny air spaces trapped between the down filaments that retard the conduction of heat from your body out to the frigid environment. If air were not such a good insulator, no amount of down would allow survival under such conditions.

Because air is such a poor energy conductor, large vertical temperature gradients can exist near the ground, particularly on clear and windless days. On such days, the land surface may experience a great deal of heating, as direct solar radiation is absorbed and converted to infrared radiation (heat energy). However, a series of thermometers mounted at different heights above the ground would reveal that air temperature falls off rapidly with height due to the poor conductivity of air.

An interesting aside: Some species of ants inhabit hot desert areas and forage during the heat of the day. The temperature at ground level would kill them after a short time of constant exposure. They continue to function, though, by frequently climbing a few centimeters up sticks or bits of vegetation to rest in the much cooler air above.

Learning Goals

  1. Students will be able to explain the process of conduction using a molecular explanation.

  2. Students will be able to explain that different materials conduct at different rates.

  3. Students will be able to identify air as a poor heat conductor (an insulator).

Alignment to National Standards

National Science Education Standards

Benchmarks for Science Literacy, Project 2061, AAAS

Grade Level/Time

Materials

Procedure

We recommend that this exercise be carried out as a demonstration. You might want to set up the in advance and start the heating as you begin to discuss conduction. Assign one student to time and record the heating for each rod.

  1. Label each rod (A, B, and C, etc.).

  2. Using a metric ruler, mark off one-centimeter increments on the rods.

  3. Using graph paper, make a data table with an entry for each rod.

  4. Turn on the hot plate.

  5. Light a birthday candle.

  6. Drip drops of colored wax on the marks on the rods.

  7. Place one end of one of the rods on the edge of the hotplate, balancing the other end on the wood block.

  8. Time how long it takes for the heat to travel down the rod, recording the time when it melts the drops of wax.

  9. Repeat with each of the other rods.

  10. Make a graph with time versus distance to record the information from the data table.

  11. Make a list indicating which rod was the best conductor to which rod was the poorest conductor.

Note: Commercial kits are available from science supply companies that can be used to demonstrate heat transfer through conduction.

Assessment Ideas

Modifications for Alternative Learners

When you're finished with the activity, click on Back to Activities List at the top of the page to return to the activity menu.