MATERIALS: Two heavy rubber plungers(one of them with small hole in it)

PROCEDURE: Push plungers together and pull them apart. This can be done relatively easily. Now tell students that you have bionic strength and can hold the plungers together while others try to separate them.Let students push plungers together and then cover the hole with your finger. Students will not be able to pull plungers apart and will be amazed at your bionic strength.

QUESTIONS:

1. Why was it so easy to pull plungers apart the first time?

2. What did actually hold the plungers together?

3. How much force was keeping the plungers together?

EXPLANATION:

The plungers were easy to separatebecause of the hole in one of them.This allowed air to enter. By covering the hole the air was preventedfrom coming in and when the students tried to pull them apart, the volume increased between the plungers, thus decreasing the pressure. The atmospheric air pressure holding the two plungers together. The force can be calculated from the total surface area of the two circles multiplied by 1kg.