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How Does the Paper Stay Dry?
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Science Area:  Physics
Concept:  Air Pressure

High And Dry Demonstration

 

Materials:

* A Cup

* A Pot

* A crumpled up piece of paper

 

Safety Considerations:

* Be careful not to spill water on the floor. 

 

Discrepancy:

Students will expect that the crumpled up paper to be wet when the cup is pulled out of the pot of water. 

 

Procedures:

 

1.   Crumple up a piece of paper and put it into the bottom of a cup.

 

2.   Fill a larger container about full with water.

 

3.   Turn the cup upside down and slowly push it into the larger container.

 

4.   Slowly pull the cup out of the container of water.

 

5.  Examine the piece of crumpled up paper.

 

Questions:

1.  What did you expect to have happen?

 

2.  Why do you think happened?

 

3.  Do you think you would have the same results if other liquids such as vegetable oil were used?

 

Explanation:

 

The reason the paper did not get wet is this:  The air remaining in the cup pushed down on the water in the container.  The push of the air on the water kept the water from moving into the cup and getting the paper wet.  This is a great visual demonstration of how great the pressure is that air exerts on other objects.  Air pressure is a tough concept to grasp because air is not something that can be seen.  It

doesn’t appear to be there, so how could it actually push anything out of the way?  Just because something is invisible does not mean that it does not exist.  This demonstration helps prove that air exists and that it can apply pressure on another object.

 

Source:  Penrose, Gordon.  Dr. Zed’s Science Surprises, Simon and Schuster, New York, NY. 1989 p.26.