You will need enough sets of each of the following materials for students to work in pairs or small groups:
- 2 clear 1-liter bottles
- Clear plastic box (shoe box or similar)
- Small plastic containers
- Liquid dishwashing soap (diluted)
- Ice water
- Warm water (you can use an electric kettle, microwave, or hot water dispenser)
- Students' science journals
- Demonstrate to the students how to dip the narrow open end of the bottle (mouth) into the soap container to form a film. Have thestudents practice. Remind students that if the film pops, they can simply repeat the procedure.
- Show students how to place the bottle in the cold water container. Remind them to place the bottom of the bottle in the water with the bottle straight upward. Have students record their observations in their Science Journals by having them sketch the bubble when the bottle is in cold water.
- Guide students to place the bottle in the warm water container. Again remind them to place the bottom of the bottle in the water with the bottle straight upward. Have studends record their observations in their Science Journals by having them sketch the bubble when the bottle is in warm water.
- Have the students move the bottles back and forth between the warm and cold water. Do they notice how the bubble behaves? When does the bubble rise above the bottle? When does the bubble lower into the bottle?
Note: For more teaching directions, see the Modeling the Behavior of Air with Bottles demonstration video for teachers.
Explain to students that convection is the transfer of heat by the movement or flow of a substance from one position to another. Temperature is a measure of the average speed or kinetic energy of molecules. By observing the bubble, students learned how the temperature of air inside the bottle make the volume of air grow or shrink.
The warm water causes the air inside the bubble to warm and expand, thus increasing the volume of air and pushing the bubble above the mouth of the bottle. The cold water causes the air inside the bottle to cool and shrink, thus decreasing the volume of air and pulling the bubble down into the base of the bottle.
As temperature of air in the bottle fluctuates between cold and warm, the bubble demonstrates the behavior of air. Students can see how the mass of air in the bottle remains the same, but the volume changes as a result of the temperature.
Discussion of the Model:
After the activity, discuss aspects of the model that are useful in explaining how temperature affects the behavior of air molecules. How is the model good at explaining what happens with air? What are the limitations of this model?
- Is the air rising or sinking when the bottle is warm? Why? (Students should demonstrate understanding that the air rises when the bottle is warmed.)
- Is the air rising or sinking when the bottle is cool? Why? (Students should demonstrate understanding that the air sinks when the bottle is cooled.)