Physics in daily life: Moving around efficiently

Europhysics News, Jul 2018

L. J.R. Hermans

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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 cheese. Etcetera. 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 Physics 2005. ~.•.;o 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.


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L. J.R. Hermans. Physics in daily life: Moving around efficiently, Europhysics News, 22-22, DOI: 10.1051/epn:2004111