Simple Air Pressure

To demonstrate the force that air pressure can exert on an object.

Piece of cardboard Paint stirrer Small orange puck

Equipment Location:

First take the paint stirrer and place it on the table with a couple of inches hanging over the edge. Once it is in place strike the part which is hanging over the edge and the stirrer should fly away from the table. For the next part put the stirrer back into the same original position and this time place the small orange puck on the end that is on the table. When you strike the over hanging part this time the puck should fly across the room. The last time you replace the stirrer place the piece of cardboard on top of the part of the stirrer that is on the table. At first just push lightly on the overhanging part of the stirrer to show that the cardboard will just rise with it. Then strike the overhanging part with some considerable force and the stirrer should break.

First when doing this demonstration be careful that when you do the parts where the stirrer and the puck go flying that there is no one in the way. Also that puck is light and will fly a good distance if it is struck to hard so you may want to use some caution. When you are doing the last part with the cardboard and you do not think you can break the stirrer or you are having trouble try using the slimmer part of the stirrer as the overhanging part as it is easier to break. Another thing is that asking questions such as what the class thinks might happen might also be a good idea.

Relevant derivations/explanations:
For this experiment we are assuming that the air pressure was 15 psi. The piece of cardboard is 12 inches by 12 inches so the force on the cardboard is almost the equivalent of 2160 pounds. Since a complete vacuum is not created beneath the cardboard that number is not entirely accurate but even if it is over by a factor of 10 it is still the equivalent of 216 pounds.