SUBJECT AREA: General Science

OBJECTIVE: To show students that atmospheric pressure is not just a downward force, but is a force acting in all directions.

MATERIALS:

1. 1-one gallon jar

2. 1-glass dish large enough to cover mouth of jar

PROCEDURE:

Fill jar completly full, so the meiniscus stands high. Place glass plate on top of the jar. making sure that no air is trapped between jar and glass plate. Then quickly turn the jar upside down. It may take a couple of times to get this right, so this should be done over a sink area.

QUESTIONS:

1. What will happen to the plate? Will it fall or stay in place?

2. What causes the plate to stick to the jar?

3. What conclusions can one draw from this?

4. Is atmospheric pressure greater than water pressure?

5. How tall would a cup have to be in order for the water pressure inside to overcome the atmospheric pressure outside?

RATIONALE:

This is an application of atmospheric pressure. Most students think that atmospheric pressure and the force of gravity have only a downward effect, the latter is true, but atmospheric pressure exerts force in all directions. This is what allows the plate to stay attached to the jar.