Activity

1. Wipe the inside of the coffee can so that it is clean and dry.
2. Cut the large balloon through one side to create one wide sheet of rubber.
3. Stretch the balloon over the open end of the coffee can and secure it with the rubber band.
4. Lay the skewer horizontally across the top of the can so that it overlaps the edges.
5. Glue the dull end of the skewer to the inside of the rubber band.
6. Tape the index card on a wall adjacent to a counter top.
7. Set the can next to the card so that the tip of the skewer is 1/4" from the card.
8. Make a pencil mark on the card to indicate the current air pressure reading.
9. Observe what happens as the atmospheric pressure changes over a period of time.

Footnote

• As atmospheric pressure increases, more force is placed upon the balloon, causing it to contract into the can and the skewer indicator to rise. As atmospheric pressure decreases, the balloon will expand out of the can and the skewer will fall. The air pressure in the sealed can represents the air pressure at the time the can was sealed with the balloon. All subsequent changes in the skewer indicate atmospheric changes (increase or decrease) relative to the time in which the can was sealed.

Assessment Ideas

• Students should keep a log of the changes in atmospheric pressure over a period of several weeks, noting whether the pressure has increased or decreased from the prior day and by how much (in millimeters or centimeters).
• Students can graph their results and compare graphs to other students.
• Students should consult their local newspapers to obtain weather forecasts to compare with their own readings.