Invisible Weight

Purpose: To understand that air has weight

Materials

• thin dowel approximately 50 cm long
• 2 balloons of equal size
• scissors
• string
• tape
• straight pin
• pencil
• science journal

Procedure

1. Cut a piece of string 25 cm in length.
2. Find the center of the dowel and tie the string at the center point.
3. Hold the dowel by the string and adjust the position of the string until the dowel is balanced on the string.
4. Blow up the balloons to approximately the same size and tie off the ends.
5. Tape the tied off end of each balloon to each end of the dowel. See diagram 1.
6. Adjust the string as needed to maintain the balance.
7. Place a piece of tape approximately 2-3 cm long on one balloon.
8. Have your partner or adult use a pin to carefully prick a hole through the tape and into the balloon. The tape will stop the balloon from popping.
9. Observe the dowel and the balloons as the air slowly escapes from the balloon.
10. Record your observations in your science journal.

Conclusion

1. Does the dowel stay balanced? Why or why not?
2. Which side is heavier? Why?