# An Experiment to Show the Mass of Air

By Terrie Schultz

Does air have mass? This simple earth science activity using balloons and a meter stick will help students understand the mass of air and that it exerts pressure.

So how about the answer to that question? Does air have mass? Well, we know that air pressure is the force that is exerted by earth's atmosphere as it presses down on a given area. Air pressure is an important concept when teaching an earth science unit on atmosphere and weather. However, since air is an invisible gas, students often have difficulty understanding the mass of air. This earth science activity will demonstrate that air has mass by showing that a balloon that is filled with air is heavier than an empty balloon.

## Materials

• Balloons
• Yardstick or meter stick
• String
• Scissors
• Two identical objects such as markers or pencils
• Tape
• Needle or sharp push pin

## Procedure

This activity can be done as a demonstration for the whole class, or groups of students can perform the experiment.

1. Before answering the question, "Does air have mass?" a simple balance can be made with a meter stick and string. Objects of the same mass hanging from the ends of the stick will balance, but if one object is heavier, the stick will tilt toward the heavier object.
2. To make the balance, take a piece of string about 12 inches long and tie it to the center of a meter stick. Attach the other end of the string to the edge of a desk or counter, allowing it to hang freely. Make sure the string is in the center and the stick is evenly balanced.
3. Demonstrate to students how the balance works by hanging identical objects from each end, such as two pencils or markers. Adjust the positions of the strings holding the objects as necessary to the stick will balance. Remove one of the objects and observe what happens. The end of the stick with the remaining object tied to it will tilt down due to the mass of the object hanging from it, and the free end will tilt up. Ask students why this happens. Because the mass of the object is pulling the stick down.
4. Blow up two balloons so that they are equally inflated, and tie a knot in the open end to prevent air escaping. Ask students why the air causes the balloons to stretch and grow bigger. It takes up space and exerts pressure on the sides of the balloon.
5. Cut two pieces of string to a length of about 12 inches, and tie a piece of string to the end of each balloon. Attach a balloon to each end of the stick, and adjust their positions if necessary to balance the stick.
6. Hold onto one of the balloons and carefully pierce it with a needle or push pin to allow the air to escape, and observe what happens. The stick will tilt down toward the balloon that still contains air. Ask students why this happens. Because the balloon containing the air has more mass than the empty balloon. The difference in mass is equal to the mass of air contained in the balloon.

Read on to learn more about the mass of air and the properties of air.

For more resources for teaching about Earth's atmosphere, see Earth's Atmosphere Vocabulary Terms.