- Ask the students to fill their bags with air by blowing them up or by pulling them through the air.
- Tie the air-filled bags, upside down, to each jar with its mouth over the opening of the jar. Wind a string very tightly around the bag and jar a few times without crossing ridges of the jar, and tie it (see #1 below).
- Ask the students to try to press down on the bags, lean on them, and rest objects on top of them. What happens? What are some explanations for this?(the air in the bag combined with the air in the jar the pressure) What other things act like this (air mattresses, tires...)?
- Have students untie the bags and put them down inside the jars with the mouth of each bag folded over the mouth of the jar and again tie them on tightly (see #2 below).
- When all are ready, ask them (at the same time) to hold the jars and pull out the bags. What happens? (It should be difficult to pull the bag out) What are some explanations for this? (air pressure is keeping the bag back).