Contents
1 Introduction 3
1.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Sky light and alike................................................................ 9
2.1 Thickness of the atmosphere . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Atmospheric absorption . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3 Blue sky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.1 Distant mountain . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.2 Color of smoke, fog or clouds . . . . . . . . . . . . . . . . . . 17
2.4 Color of the sun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.5 Flattening of the low sun and moon . . . . . . . . . . . . . . . . . . . 21
3 Water and light ...........................................................29
3.1 The color of water . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2 Glitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3 Caustic network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.4 The rainbow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4 Bubbles ................................................................................39
4.1 The sound of mountain streams . . . . . . . . . . . . . . . . . . . . . 39
4.2 The sound of boiling water . . . . . . . . . . . . . . . . . . . . . . . . 43
4.2.1 Surface tension . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.3 The sound of a fresh, hot cup of instant coffee . . . . . . . . . . . . . 45
4.3.1 Speed of sound . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.3.1.1 sound in air . . . . . . . . . . . . . . . . . . . . . . . 49
4.4 A bubble bath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.4.1 Effect of bubble expansion . . . . . . . . . . . . . . . . . . . . 55
4.4.2 Effect of evaporation . . . . . . . . . . . . . . . . . . . . . . . 56
5 Bernoulli .......................................................59
5.1 Bernoulli . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.2 Shower curtain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.3 Boat trip through the channels of Delft . . . . . . . . . . . . . . . . . 60
5.4 Water flowing over an elevation in the river bottom . . . . . . . . . . 62
5.5 Why can air planes fly? . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.6 Top and back spin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.7 Emptying container . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.8 Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
6 Heat
6.1 Chinese egg roll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
6.2 Frozen slice of bread . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6.3 Black or white radiator? . . . . . . . . . . . . . . . . . . . . . . . . . 76
6.4 Sipping Bird . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
6.5 Milk in the coffee and leaves in the tea . . . . . . . . . . . . . . . . . 79
6.6 Freezing lakes and channels . . . . . . . . . . . . . . . . . . . . . . . 82
7 Mechanics at work
7.1 Catastrophe Toy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7.2 Bungee jumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.3 What is the shape of a suspended cable? . . . . . . . . . . . . . . . . 96
7.3.1 Problem formulation . . . . . . . . . . . . . . . . . . . . . . . 96
7.3.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
7.3.3 Lowest point of the rope . . . . . . . . . . . . . . . . . . . . . 98
7.3.4 Intermezzo: the suspended rope as Variational Principle . . . 100
7.4 High tide, low tide . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
7.5 Fire hose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
7.6 Falling Pencil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
7.7 Capillary pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Introduction
Who loves nature observes her the same way he/she breathes and lives: from a native
inner drive. This is the openings sentence of Prof. Dr. M. Minneart’s series of
three books about the physics of our environment. Minneart (a Belgium Physicist
who died in 1970) published his books in 1937 for the first time. His books have been
translated in many languages and are still in press, showing that a basic understanding
of the physics of the world around us is still popular. This can also be seen in
the weekly science sections of the better newspapers: many of them have a column
that deals with questions from its readers asking for an answer to some remarkable
observation. In many cases the answer is found in physics of every day life. Some of
the questions are for a physicist rather obvious, other are difficult to answer. In many
cases the observation seems trivial, but the answer can push one deeper and deeper
into the world of physics. And as always, with an increased level of understanding
the phenomena in question gains in beauty. This course is set up with the idea
that the world around us is full of beauty and that an appreciation of it is deepend
as the understanding in terms of physical reasoning is brought to a higher level.
Furthermore, it is just fun to think about what we see, hear, feel and try to find an
explanation.
Since Prof. Minneart’s book saw the light many others about the physics of daily
life have appeared. Some relatively superficial, others just fun reading but also quite
a few that try to give answers and insight based on sound physical reasoning. To
name a few
De Natuurkunde van ’t Vrije Veld, 1, 2 & 3
Dr. M. Minnaert
B.V. W.J. Thieme & Cie -Zutphen
Clouds in a Glass of Beer - Simple experiments in atmospheric physics
C.F. Bohren
John Wiley, 1987
Color and Light in Nature
D.K. Lynch and W. Livingston
Cambridge University Press, 1995
De Wetten van de Vliegkunst - over stijgen, dalen, vliegen en zweven
H. Tennekes
Aramith, 1992
The flying Circus of Physics - with answers
J. Walker
John Wiley, 1977
Alledaagse Wetenschap
K. Knip
Uitgeverij Contact Amsterdam, 2000
Finally, I would like to mention the ’Lectures on Physics’ by Richard Feynman. Although
this is not written as a series about physics in daily life, it has some nice side
steps to it but foremost it is excellent in explaining and providing inside of the basics
of physics.
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