\Does Air Have Mass?
There's a yardstick suspended from the ceiling, and we used balloons (one empty and one full) to conduct the experiment. Then, we checked the mass on a balance. We placed two balloons on the balance. Then, we added air to one.
Conclusion: Yes, air has mass!
Disclaimer: You gotta love science! The yardstick experiment should have worked, but in reality, it didn't. We had a hard time getting the yardstick to balance, so we held the string to try to balance it. When we did this, the balloon with air didn't demonstrate that air has mass like it should have. My students hypothesized that when we held the string in our hands to balance the yardstick, we actually balanced the balloons too. That's why we checked the experiment with a scale. We found a video on youtube and watched how it was supposed to work. Then, we had a wonderful discussion on the importance of conducting an experiment correctly before drawing conclusions.