Session 1: Preparation for the concept of lift

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Objective 1: To show that when air is moving, some unexpected effects are produced

Objective 2: To arrive at the conclusion that when air is moving faster it pushes less and vice-versa

 

Explanation

The Bernoulli theorem considers conservation of energy law and is too complex to explain to young students. The principle is that, in absence of compressibility effects, when a fluid is moving an increase of pressure will generate a decrease of velocity and vice versa. If this may be too complex to explain to them we can at least show them experiments where this “exchange” between velocity and pressure generates surprising effects.

Material

• A4 sheet of paper
• Air balloons
• A little bit of sand
• A kebab stick
• String

Maximum duration

45 minutes

Main question to be asked

What is the difference if air is moving?
If the velocity increases does the air push more or less, than if the air is not moving?
Pressure and pushing: can you relate this two terms (for a 11 Year old ?)

Introduction/Starters

These three objects are flying but not for the same reason, can you explain the differences?

Main activities

Experiments: Change of velocities

A. Phase of observation

- Paper experiment

• Take with two hands 1/2  sheet of A4 paper
• Put your mouth just on the upper part of the sheet and blow on it. What do you observe?

- Balloons experiment

1. Blow up two balloons,
2. Before closing them put a little bit of sand in it, so they are not moved by small draughts
3. Then attach to each balloon a string and attach them to a wood kebab stick. The balloon should be separated by around 4 or 5 cm
4. Blow between the two balloons
5. What do you observe?

Possibly experiment with a funnel.

B. Phase of discussion:

Can you find out what is common between those two experiments?

Conclusion/Plenary

The conclusion is that, in the two exp4eriments, when we are blowing, we give to the air a certain velocity.
The air has a higher velocity on the upper part of the piece of paper and in between the two balloons.
Air does not move on the lower part of the sheet of paper and on the external part of the balloons.

The fact that the sheet goes up where the air is moving and the fact that the balloons stick to each other where the air is moving, demonstrate that the air is pushing more … has more pressure when it is not moving and the air is pushing less when it is moving.

This was discovered by Daniel Bernoulli in 1738, and is the basic principle of the lift of an airplane.

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