Air Has Mass

INTRODUCTION

The purpose of this experiment is to illustrate that air does indeed have mass.

MATERIALS

• Yardstick
• Balloons
• String

WHAT TO DO

1. Suspend the yardstick from the ceiling or some other object that allows it to be freely suspended. Make sure that the string is at the exact center (on a yardstick this is at 18 inches). Adjust the string so the yardstick is evenly balanced and hangs horizontally.
2. Tape a balloon to either end (the balloons should not be blown up). Make sure the yardstick is still balanced horizontally.
3. Remove one balloon, blow it up, and replace it.

QUESTIONS

1. What happens to the yardstick when the blown-up balloon is placed on one end that is different from when the neither of the balloons was blown up?
2. What caused this change?

SUMMARY

The mass of the air in the balloon causes the yardstick to tip. The reason students do not feel the weight of the air on them is that they have never been without it!

EXTENSION

1. The density of air is 1.225 kg/m³ at 15 °C and sea level. Calculate the approximate volume of air in the classroom in cubic meters. Using the density of air, what is the mass of the air in the classroom?

SOURCE

"Science Is." Susan V. Bosak. Scholastic Press, 1991. ISBN 0-5907-4070-9

© S. Olesik, WOW Project, Ohio State University, 1999.