Physics in daily life: Moving around efficiently
Moving around efficiently
0 L,f.R Hermans, Leiden University , The Netherlands
phenomena in everyday life, and being able to explain them to the layman. This has some extra relevance in view of the upcoming World Year of Physics 200S.This "Physics in daily life ..."column is aimed at doing just that. Since it will span a wide variety of phenomena, most of which are outside the research expertise of the author, he welcomes comments, additions or corrections, especially from readers who happen to be more familiar with the topic.
... Erratum: This figure,
omitted from the first
Physics in daily life column,
"The human engine: How
to keep it cool,"IEPN 34/4,
page 153] demonstrates
schematically that each 100
Wof released heat that has
to be compensated by
evaporation requires a glass
of water (0.181) per hour.
400 W continuously in terms of oil consumption per day, we find
pretty much exactly one litre per day, given that the heat of com
bustion ofmost types of oil and gasoline is about 35 MJ per litre. In
other words: if, for the sake of the argument, we ride 24 hours con
tinuously, without getting off our bike, we have used the equivalent
of 1 litre of gasoline in keeping moving. How far will that get us?
That, of course, depends on the type of bike, the shape ofthe rider,
and other parameters. If we take 20 km/h as a fair estimate, the 24
hours of pedalling will get us as far as 480 km. In other words: a
cyclist averages about 500 km per litre.
That's not bad, compared to our car, or even a motorbike. So,
we should all ride our bike ifwe want to conserve energy? Careful,
there is a catch here. We have been moving on food, not oil. And it
takes a lot more energy to get our food on the table than its energy
content may suggest. A glass of milk, for example, takes roughly 0,1
litre of oil, a kg of cheese roughly 1 litre. It's because'the cow has to
be milked, the milk has to be cooled, transported, heated, bottled,
cooled again, transported again, etcetera. Same (or worse) for the
Conclusion: Riding our bike is fun. It's healthy. It keeps us in
shape. And if we have to slim down anyway, it conserves energy.
Otherwise-I hate to admit it: a light motorbike, if not ridden too
fast, might beat them all.
surface interactions, and nuclear spin conversion in
polyatomic molecules. In the 1990s he served as a
mem,~~:a:::~_ ber of the EPS council. Presently he chairs the
National Steering Committe for the World Year of
About the illustrator
Wiebke Drenckhan (26) is currently
- doing her PhD in the "Physics of
Foams" in Trinity College Dublin, Ire
land. She has studied and worked in
Germany, USA, New Zealand and
France, being largely supported by the
German National Merit Foundation.
Additionally to taking a scientific
approach to the world, she likes to
capture its oddities in cartoons.