Daniel Bernoulli was a Swiss scientist ( ) who analyzed the pressures involved with fluids. He found that stationary fluids such as air and water exert pressure in all directions. When a fluid is moving slowly it has a higher pressure or more force; when that same fluid is moving faster it has lower pressure or less force.

Review the properties of fluids. Do fluids move? Do fluids exert pressure? What activity did you do that shows that air exerts pressure? Paper towel in the glass.

You will be investigating how air pressure changes. Each student will get a 5cm x 15cm strip of paper. Place paper just below the bottom lip. What do you think will happen if you blow over the top of this strip of paper?

Make predictions. Test your predictions by blowing over the strip of paper and observing what will occur. What happened to the paper? Why do you think the paper lifted?

Air moves quickly over the paper, causing low pressure. It is less dense than air sitting under the paper strip. Moving air has less pressure than air that is stationary. This means that the air under the paper more dense and causes higher pressure.

This high pressure has greater force and, therefore, exerts this force on the paper, causing it to lift.

Each student gets an index card. Fold card in half and stand it upright on the table. Blow the card off the table by blowing into the “V” part of the card. (Through the tunnel).

What did you observe when you were blowing underneath the card? What properties does stationary air have? When blowing underneath the card, what is different about the air underneath the card compared to the air above the card? Why do you think the card did not blow off the table?

The stationary air exerts more pressure than flowing air exerts. The faster the flow of air, the lower the pressure it exerts. By blowing underneath the card, an area of low pressure is created, so that pressure above the card is greater. This is why the card pressed down against the table.

Funnel and ping pong ball. Do you think I can pick up the ping pong ball with the funnel without sucking through the funnel or touching the ball? What are some ways we could do this? Now pick up the funnel by the stem, place it over the ball, and blow through the stem. Lift the funnel while blowing.

How did I pick up the ball? What happened when I stopped blowing into the funnel? What happens to the air in the funnel when I blow? -the air moves fast. What is the fast moving air creating? - low pressure

What is the difference between the air on the inside of the funnel and the air on the outside of the funnel when I am blowing? - low pressure inside from moving air, high pressure outside from stationary air.

Note- when blowing through the funnel, low pressure is created, especially at the point where the stem meets the cone of the funnel. Here, the fastest flow of air occurs because the air molecules suddenly have more space to move about. The faster the flow of air, the lower the pressure.

The stationary air around the funnel has greater pressure of force. Therefore, a partial vacuum is created. This is why the ball is sucked into the funnel.

Practice yourself.

Tape thread to two tennis balls and hold the tennis balls about 3cm apart. What do you think will happen if I blow in between the two balls? Test predictions.

What did you observe as I blew between the balls? What did I create between the balls by blowing? -low pressure by moving air. What is the different about the air between the two balls and the air surrounding them? - the air between the two balls has lower pressure, the stationary air around the balls has higher pressure.

When blowing between the two balls, some of the air molecules are pushed away, creating a lower pressure. The moving air also has lower pressure. The stationary air surrounding the balls exerts greater pressure, thereby pushing the balls against each other.

The ideas about air pressure were first discovered by Daniel Bernoulli, and are referred to as Bernoulli’s Principle. Activity sheet 2.4.1