BioEd Online

Teacher Background

The molecules in air (and in all gases) are constantly moving, but the amount of movement depends on temperature. At higher temperatures, molecules are more active. They bounce off one another and off the sides of a container with more energy. At lower temperatures, molecules move less and bounce with less energy. A given number of gas molecules will take up more space when warm (because of more energetic “bouncing”) than the same number of molecules at a lower temperature. These characteristics account for much of the air movement that we can observe, both indoors and outdoors. Air currents develop when there are differences in temperatures, because higher-energy (“bouncier”) warm air molecules rise and lower-energy cool air molecules sink.

Objectives and Standards

Concepts

• Heat causes the molecules in air to become more active and push harder against the sides of a container.

Science, Health, and Math Skills

• Predicting

• Observing

• Drawing conclusions

Materials and Setup

Teacher Materials (see Setup)

• 1 liter of cold water (or ice cubes)

• 1 liter of warm tap water

• 1 liter of room-temperature water

• 1 tea candle and matches, hotplate, warming tray, or warm towel

• dishwashing liquid and glycerin for bubble solution

Materials per Group of Students

• 3 clear, wide-mouth plastic cups, 9-oz size

• prepared bottom half of an aluminum soft drink can

• crayon or marker, blue

• crayon or marker, red

• plastic petri dish or shallow bowl/saucer

• copy of “My Observations” student sheet

Materials per Student

• safety goggles

Setup

1. Trim aluminum soft drink cans prior to class. Cut each can approximately in half (scissors work well) and save the bottom section. You will need one bottom section per group of students. (Discard or recycle the top halves.)

2. Make sure that the cut edges of the cans are relatively smooth OR cover the edges with tape.

3. You will also need to prepare “bubble solution” if you do not have any available. To make one gallon of bubble solution, which will keep indefinitely, mix together one gallon of water, one cup of Ivory or Dawn dishwashing liquid, and 1/4 cup of glycerin (from the drugstore).

Procedure and Extensions

1. Challenge your students to predict whether warm air and cold air behave differently. Ask, Do you think air will sink or rise if it is warmed? Write students’ predictions on the board or have each group make its own prediction.

2. Set up a station from which the Materials Managers can pick up the following supplies for their groups: one prepared can, one shallow dish or bowl with bubble solution, one cup half-filled with warm tap water, one cup half-filled with ice water (include a few ice cubes), and one cup half-filled with room-temperature water.

3. Demonstrate how to tip the open end of a can in the bubble solution to create a thin film. Have students predict what might happen to bubble film when the can is placed in room-temperature, warm, and cold water. They should draw their predictions on their student sheets. Have students dip the open ends of their cans into bubble solution. A film of solution will be visible across the top of the can. Direct each group to place its can in one of the cups (cold water, warm water, or room -temperature water). Let students observe the bubble film for about a minute. Ask, What is happening to the bubble? What does this tell us about the air inside the can?

4. Have students record their observations on the “My Observ­ations” sheet. Then have each group make a new bubble film and place its can in one of the other cups. Have students record their results before placing and observing the can in the third cup.

5. Discuss students’ predictions about the behavior of warm and cool air, in light of their observations. Ask, What do you think will happen if we heat the air in the can even more? In a demonstration area, dip another can in bubble solution, then heat it using a lighted candle, hotplate, warm towel, etc. (The bubble will bulge much more dramatically than students saw in their previous trials.)

6. Discuss the students’ discoveries about air movement and encourage them to think about what might be happening with the air inside the classroom. Ask, What happened to the air inside the can when it was placed in cold water? In warm water? Follow by encouraging a general discussion. Ask, Where are the sources of different air temperatures in the room? What will happen if the air in one part of the room is warmer than air in other parts?

Extension

Let students use bubbles to study air movements in other ways. For example, have them gently blow bubbles up into the air. Have them observe where the bubbles travel. Ask, Do the bubbles eventually fill the room? Do they move upward or downward? (An inexpensive bubble blower can be made by removing the bottom from a paper cup.)

Handouts and Downloads