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Activity Number 4 - An Experiment

Purpose

To show that air exerts pressure.

Materials

  • A thin rectangular board, for example a strip of thin plywood or paneling which is about a half metre long and 8 to 10 centimetres wide
  • One full-size newspaper
  • Ruler
  • Paper and pencils

Method - Part one

Place the board on the table with slightly less than one half of the board hanging over the edge. Open the newspaper and lay it flat over the section of the board on the table. Ask your students what they think will happen to the paper if you strike the part of the board that is hanging off the table. Then strike the protruding part of the board as hard as you can. What happens to the paper? Does it move? Does the board flip up as some of your students thought it would?

Observations

The paper remained in place.

Conclusion

The paper did not move because the air pressure that is exerted downward held it in place. Since the paper is flat against the table, there is no air beneath the paper to counteract the pressure from above. If you hit hard enough, the board will break.

Method - Part two

Ask your students what will happen if you slowly push down on the protruding board. Then push down on the board slowly. What happens to the paper this time?

Observation

The paper slowly rises off the table.

Conclusion

Air exerts pressure on all surfaces that it touches. When an air space is created under the paper, the pressure exerted by that air counteracts the pressure from above and the paper is no longer held in place.

Final Activity:

Have your students calculate how much pressure was being exerted on the paper in part one of this experiment. They can measure the length and width of the newspaper in centimetres, then multiply the 2 measurements to get the surface area. Ask them how many kilograms of air are pressing down on that sheet of newspaper using the average sea level pressure of 1 kilogram per square centimetre.

Martha Suarez, Stephen F. Austin, University Nacogdoches, TES Course, 1994

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