Abstract: (max. 700 characters incl. spaces): A kite can`t possibly fly

Project description for participation
in the European Science on Stage festival
from 25 – 28 April 2013 in Słubice – Frankfurt (Oder)
Abstract: (max. 700 characters incl. spaces):
A kite can’t possibly fly in the blow of a fan but a balloon can stay on balance in the air for a
long time. How to explain that?
The core of this project is to initiate pupils to a scientific reasoning, using various
experiences and observations.
Equipped with hairdryers and filled with curiosity, the pupils carried out several experiences
to discover the basic principles of the fluid mechanics, and to tackle such a complex world
that is the one of “turbulences”.
The pupils looked for possible applications to their work. They tried to better understand the
world surrounding them and to create new flying objects such as jellyfish, spiders, cats,
superheroes and many other things born from their imaginations.
Involved disciplines: physical Sciences, mathematics, Natural Sciences and arts
Keywords: turbulence
Age group (Age of the students): 13-14 years
Materials used in this project: balloons, styrofoam objects, hairdryer
What is innovative about your project?
Use the scientific method to discover new concepts
What can other teachers implement from your project in their class?
Mathematics teacher, Natural Sciences teacher, arts teacher
Personal quotation concerning your project: Supervision of students
Project description: (max. 12.000 characters incl. spaces / approx. 2,5 pages)
1) Introduction:
Our little scientific journey starts with a cartoon picture. We saw on it a famous caracter making fly a
kite in the blow of a fan.
Despite our numerous tries, we never managed to succeed the same more than a few seconds. But if
we replace the kite by a balloon, everything become easier: the balloon is flying over the fan, very
stable, like trapped in the air flow.
After our first enthousiastic discoveries, we tried to replace the balloon by other objects, in
particular polystyrene balls. And to have a more powerful air flow, we replace the fan by an air
dryer. The astonishing result is that the balls stay at balance even the hair drier was tilted!
What strange force can keep the ball up?
All the team starts to investigate:
- How is the air flow around the ball?
- Why is the ball sometime spinning?
- Have the size or the shape of the object any impact?
Even if the theoretical explanations are obviously too complicated for the pupils, we decide to
investigate with simple experiments to understand what’s going on.
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We focus on the following question:
How a ball can fly in the air blow of a hair dryer?
2) Look for hypotheses:
Everyone try to have an idea and to represent the blow of the air around the ball. Each pupil has to
explain with their own words what they represent. For example : a vortex can keep the ball in the
center.
3) Experimental studies
Our next step was to look for a maximum of experiments, feasible in our school, to understand the
physical phenomena involved:
Experiment 1: study on the volume and the mass of the objects
Experiment 2: study of the shape of the objects
Experiment 3: influence of the orientation of the hair dryer
Experiment 4: Air action on hanging balls
Experiment 5: discovery of the Ventury effect
Experiment 6: influence of a plane surface closed to the flying objects
Experiment 7: air speed measurements
Experiment 8: how to make the air blow visible: use of smoke and laser
4) Solution of the problem
With all these experiment, we are now able to answer our question: how a ball can fly in the air
blow of a hair dryer?
We understood easily that the air, moving at a high speed, is acting on the inferior part of the
object, which counterbalance the weight. But we still have to understand the stability, even if we
push the ball a little.
What prevent the ball from falling when we put it away from the center of the blow, where the
speed is maximal?
All of our experiments have confirmed that the air goes around the ball and accelerates. We saw
that the moving air at the object surface is creating a depression (Ventury effect) which tends to
bring the ball back to the center.
Why are the spheres flying better?
The advantage of a sphere is that it is showing the same surface to the blow even if it is spinning. It
contributes to its stability.
Why is the kite not flying ?
A kite has no close symmetry of a sphere. If it goes away from the center, the air can’t go around it
anymore so that the counterbalance is decreasing: it falls.
5) Looking for new flying structures
The idea is to find funny new flying structures. We work in collaboration with the art teacher.
Here are some examples:
- « the balloon family »: we tie up 4 balloons so that all 4 can be, one over the others, in the air
blow. This structure is very stable: when one balloon is going away, the others help to put it back in
the blow.
- more artistic shapes have been considerer : the “flying spider or medusa“ for example
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6) Consequences in the day life
We finally look for situations in the day life which can be connected to our work:
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How the air can close a door?
Why the high speed cars are always close to the ground?
Why is a car attracted by a truck as it is overtaking it?
Why is a stopped car moving when another car is passing?
How a football player can mark by bypassing the « wall »?
Why can the windows of close buildings explode when a hurricane is passing?
How a plane can fly?
7) Connection with other disciplines and scientific contacts
The mathematics teachers work with the pupils on the computation of surfaces and on the
Reynolds equation which gives the different turbulence flows.
With the biology teacher, we look for living forms which use the air blow or are able to adapt to
extreme conditions.
The art teacher helps to design original new flying structures.
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