Magical bubbles and
soap films
Frank Kühnemann
Physics Department
German University in Cairo
Magical Bubbles & Soap Films – March 20, 2010
Water Droplets – Walking over Water
Films and Bubbles
Minimal Surfaces: Physics, Mathematics and Architecture
Films and Bubbles in Space
Magical Bubbles & Soap Films – June 8, 2011
1
Water drops
Magical Bubbles & Soap Films – June 8, 2011
What gives the droplet its spherical shape?
Water molecules attract each other
(surface tension)
surface like a flexible membrane,
trying to reach a minimum size
A „minimum problem“:
For a fixed amount (volume) of water,
what will be the shape with the
smallest surface?
Calculation and experiments:
The Sphere
Magical Bubbles & Soap Films – June 8, 2011
2
„Walking on water“
Magical Bubbles & Soap Films – June 8, 2011
Adding soap to the water
Tensid molecules have two different ends
Soap layer at the surface
likes water
(hydrophil)
dislikes water
(hydrophob)
molecules
Micelle in water
Smaller force between the detergent molecules – reduced surface tension
Magical Bubbles & Soap Films – June 8, 2011
3
Soap bubbles
Repulsion between the soap
particles breaks the film
A bubble
Gravity pulls down the
water molecules
water molecule
Soap particle
Magical Bubbles & Soap Films – June 8, 2011
How to make really large films?
Martin Rutgers
Ohio State University
Magical Bubbles & Soap Films – June 8, 2011
4
How to make really large bubbles?
http://www.worldrecordsacademy.org/games/img/free-floating-bubble-90306.jpg
Magical Bubbles & Soap Films – June 8, 2011
Colourful soap bubbles
Magical Bubbles & Soap Films – June 8, 2011
5
Waves on the water
Wavelength = distance
between two crests of the wave
Magical Bubbles & Soap Films – June 8, 2011
Light waves
Different colors of light have different wavelengths λ.
They are smaller than 1/1000 of a mm (0.001 mm)!
(One sheet of printer paper: about 0.1 mm)
λ = 0.0004 mm
λ = 0.0007 mm
Magical Bubbles & Soap Films – June 8, 2011
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Light waves and soap films
Light hits the film
partial reflection at the front and the back
Magical Bubbles & Soap Films – June 8, 2011
Light waves and soap films
For very thin films, the two reflected waves interact
= „Interference“ between the reflected waves.
The thickness of the film controls which colors
can be seen in the reflected light.
Magical Bubbles & Soap Films – June 8, 2011
7
Light waves and soap films
The wall of the soap bubble is only some 1/1000 mm thick!
Magical Bubbles & Soap Films – June 8, 2011
What to learn from soap bubbles? Geometry
Surface for one enclosed volume?
Sphere
Surface for two enclosed volumes?
Two spheres in contact
Contact area is not plane:
bent towards the larger sphere
Magical Bubbles & Soap Films – June 8, 2011
8
How to build the perfect honeycomb?
How to enclose the largest volume with the minimum wall material,
one cell next to the other?
honeycomb
Soap bubbles enclosed between
two plates
Magical Bubbles & Soap Films – June 8, 2011
What is the smallest area for a given frame?
Which form yields
a minimal surface
for a given frame?
Plateau problem
(J.A.F. Plateau)
Calculation is
complex
make a soap
film model!
Moebius
Clover leaf
Magical Bubbles & Soap Films – June 8, 2011
9
Architecture: Light-weight, stable structures
Sebastian Demuth
For the minimum surface all forces are balanced
light-weight frame is required
Soap films replace(d) computers!
only a
Magical Bubbles & Soap Films – June 8, 2011
Frei Otto: Minimal surface principles
Wire models
Soap films
Multihalle Mannheim
Magical Bubbles & Soap Films – June 8, 2011
10
Munich Olympic Stadium
Magical Bubbles & Soap Films – June 8, 2011
Sharm El Sheikh Airport, new terminal
Magical Bubbles & Soap Films – June 8, 2011
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Prophet‘s Mosque, Medina, Saudi Arabia
Magical Bubbles & Soap Films – June 8, 2011
Saturday Morning Science - Water in space
What happens when gravity becomes negligible?
Astronaut Don Pettit, Ph.D.,
„Saturday Morning Science“
Experiments aboard the
International Space Station, February 2003
http://spaceflightsystems.grc.nasa.gov/WaterBalloon/#ISS
Magical Bubbles & Soap Films – June 8, 2011
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Saturday Morning Science - Water in space
Air bubble in a water droplet, resting on a plantlet leaf
Magical Bubbles & Soap Films – June 8, 2011
Saturday Morning Science - Water in space
What happens when gravity becomes negligible?
Water drops
Magical Bubbles & Soap Films – June 8, 2011
13
Back on Earth
What happens when a raindrop hits a soap bubble?
… or other intruders?
Magical Bubbles & Soap Films – June 8, 2011
A summary
„Physics?
That‘s just an advanced form of playing…“
http://www.scenicreflections.com/download/208409/Earth_in_Soap_BUBBLE_Wallpaper/
14
The new place:
Freiburg
Fraunhofer Institute
for Physical
Measurement Techniques
Freiburg
Freiburg
Thank you!
See you soon!
http://www.scenicreflections.com/download/208409/Earth_in_Soap_BUBBLE_Wallpaper/
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