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When a car brakes sharply, the occupants and luggage are thrown forward. But what happens to a balloon filled with helium? Does he also fly in the direction of the windscreen? Heinrich Hemme presents this and 99 other riddles in his book. The Aachen Professor of Mechanical Engineering and Mechatronics and permanent bdw columnist covers all physical fields - from mechanics to hydraulics and electricity to the theory of relativity.

Most of his "head nuts" sound simple, but they turn out to be pretty tricky. Why do electric egg cookers need less water the more eggs you want to cook with them? When can you rather drink the hot coffee: If you pour the cold milk or if you let it cool down first? What is the total resistance of twelve resistors located on the edges of a cube? Even the physically educated reader will be glad if he can crack a part of the tasks without any doubt. Fortunately, Hemme solves his puzzles in the second part of the booklet and explains the physics behind it in a clear and non-verbose way - a treat for anyone who enjoys the little secrets of everyday life and apparent paradoxes.

By the way, the balloon filled with helium does not rush forward like the other objects in the car, but flies backward. Because the car is filled with air that is heavier than helium: It exerts on the balloon a buoyant force that is greater than the inertial force that pushes him forward. Wolfgang Blum

Heinrich Hemme DUZENTRIEB CONTRA EINSTEIN rororo, Reinbek 2008 192 p., € 8.95 ISBN 978-3-499-62323-3



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