# Bernoulli experiments with sheets of paper

##### Class practical

This quick activity could be used as a starting point for discussion of atmospheric pressure.

#### Apparatus and materials

For each pupil

Thin paper (up to 80 gsm), 2 sheet

#### Procedure

a Hold two pieces of thin paper vertically a short distance apart and blow down into the space between them.

b Hold one end of a small sheet of paper in both hands. Keep the held edge horizontal while the other end sags under its own weight. Blow steadily over the top of this horizontal edge.

#### Teaching notes

1 It seems amazing that the two sheets of paper move closer together. In both cases, pressure is reduced where air is moving quickly. This is called the Bernoulli principle.

2 Some squeaker toys make their noise with blades like those two sheets of paper. Vocal chords act in the same way.

3 The diagrams below illustrate how a plane takes off. The moving plane starts a vortex of air circulating round the wing. The vortex combines with the general flow of air past the plane so that the combined flow pattern leads to faster air above the wing and hence less pressure above the wing. The higher pressure below the wing then creates lift.

The image below shows a cross-section through the wing.

This experiment was safety-checked in March 2005