MATERIALS:

1. Two empty soft drink cans.

2. About two dozen straight drinking straws.

PROCEDURE:

1. Spread the straws parallel to each other on the table and leave about 1/2 to 1 cm gap in between them.

2. Place the two cans upright about 2 cm from each other on the straws and show the students that they can easily move closer or further apart.

3. Blow in between the two cans with a short hard puff.

4. Now spread the two cans about 5 cm apart. Blow harder.

5. Now place the cans about 20 cm apart. Take a deep breath and blow a constant stream of air on the RIGHT SIDE of the LEFT can and move your head towards the right, while constantly blowing.

RATIONALE:

This demonstration illustrated the Bernoulli principle. As the speed of air increases, the air pressure decreases. Blowing in between the cans created a flow of air and thus a lower pressure compared to the stationary air on the other side of the cans. It is this lower pressure that drew them together. Theoretically, the cans could be placed an infinite distance away from each other and still be drawn together, as long as a constant flow of air on one side of one can moves along with it, to move it to the other can. Indeed, the faster the flow of air, the lower the pressure it exerts. But for the cans that were placed 20 cm apart, only a constant flow that could move the can, was necessary.

APPLICATION: Aviation ( ie. airplane wings)