Is Air a Fluid?

Modified with permission from Convection: A current event from the Lawrence Hall of Science, Great Explorations in Math and Science

Type of Lesson:Hands-on Activity/Demonstration

Time Needed:20 Minutes

National Standards Addressed

Physical Science, Grades 5 to 8: Heat moves in predictable ways, flowing from warmer objects to cooler ones, until both reach the same temperature.

Earth and Space Science, Grades 9 to 12: Heating of Earth’s surface and atmosphere by the Sun drives convection within the atmosphere and oceans, producing winds and ocean currents.

Quick Summary of Lesson

This activity provides an introduction to air as a fluid. Any substance that flows is considered a fluid. This includes such things as water, shampoo, sunscreen, and even honey. Although not necessarily obvious, even gases, such as air, can be classified as fluids. This activity will allow students to ‘pour’ a gas and watch the results.

Materials for each group of 2-4 students

Baking soda
500 ml beaker or glass jar of similar size
Candle (a small votive candle is ideal)
Strip of poster board or cardboard about 12" by 3" (old file folders work well)


1. Discuss the physical properties of a fluid with students. Be sure to include the idea that fluids can be poured. Ask students if they think air is a fluid. Ask how it could be demonstrated.

2. Fold the poster board or cardboard lengthwise. (See illustration)

3. Place the candle on a plate and light the candle.

4. Put about a tablespoon of baking soda in the glass jar or beaker.

5. Pour about 1/4 cup of vinegar in the jar or beaker. (The vinegar and baking soda will react immediately filling the jar with carbon dioxide gas.)

6. When the fizzing subsides, hold the poster board "funnel" at an angle so that one end is near the candle flame and the other end is slightly higher. (See illustration)

7. "Pour" the gas in the beaker or jar down the funnel. The flame will go out in a second or two.

Notes to the Teacher

1. Because of the involvement of fire and matches, you may choose to do this as a demonstration for younger students.

2. Discuss with the class what happens when the vinegar and baking soda are mixed. (The mixture froths and bubbles, producing carbon dioxide.)

3. Explain to the class how the flame was extinguished. (There was no more oxygen available for the flame, so it went out. Pure carbon dioxide is denser than air, so it flows like a liquid from the jar or beaker along the funnel. Carbon dioxide is used in fire extinguishers because it is effective at smothering flames.)

Need More Information? Try Using Windows to the Universe

Please use these links for further ideas or more information:
The Earth's Atmosphere
Last modified October 9, 2002 by the Windows Team

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