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Physics For Entertainment

Maybe the last name 'Perelman' in not unfamiliar to you. Recently, the Russian mathematician Grigori Perelman (1966-) became world-famous for two very important things: for having solved the century-long PoincarĂ© conjecture (confirmed in 2006), and for rejecting  a one-million dollars price for solving that problem. He was awarded the prestigious Fields medal in mathematics for that achievement.

Another 'Perelman', this time Yakov Perelman (1882-1942, back in the Soviet era, became a famous populariser of mathematics, physics, mechanics and general science subjects.

What's the relation between both? More than their last names suggest, because they lived in different times.

But there was a small gift that Grigori's father handled to his son: it was a copy of Yakov's book Physics for Entertainment that Grigori admitted "it inspired his interest in mathematics".

Physics for Entertainment -a book by Yakov Perelman about the science of our everyday activities and phenomana.Physics for Entertainment is not a mathematics books, nor a physics book; it is a book about how every physical activity in our surrounding has an explanation. It is a book about how many times our senses deceive us; about how not always a satisfactory explanation is also the best explanation.

At the end of the book, Y. Perelman asks many review questions. Here follows some of them. How many can you can answer?

  • When do we move round the Sun faster?
  • Which points in a train going forward move backwards?
  • Why do we lean forwards or shove our feet under a chair when we get up?
  • What is the difference between running and walking?
  • How should one jump off a moving car?
  • Does a body weigh more or less when falling than when at rest? Must everything fall back to Earth?
  • Can you weigh things right on faulty scales with correct weights, or on a properly calibrated balance, but with wrong weights?
  • Why doesn’t a skier sink into soft snow?
  • Why is it pleasant to loaf in a hammock?
  • Why does a kite fly?
  • Does a stone continue accelerating all the time it drops?
  • What is the greatest speed a parachutist making a delayed jump can achieve?
  • Why does a boomerang boomerang?
  • Where is a thing heavier? Closer to the equator or to the poles?
  • When a seed germinates on the rim of a spinning wheel, in which direction does it stem?

The atmospheric self-winding clock is a pseudo perpetual motion machine.What is perpetuum mobile? For centuries and centuries inventors, 'mechanicians', physics and science dilettantes, have searched for a machine that never stops, or a machine that propels itself. This is the holy grail of the mobile mechanisms.

It has been mathematically proven that due to the loss of heat because of the friction of the moving parts, no machine can perpetually run without external supply of energy.

However, there is an alternate approach to the continuous supply of energy: this is the unceasing variation  of the atmospheric pressure and atmospheric temperature. Based on that variables, some clocks are built to wind themselves using the surrounding ATMOSphere.

  • Where does a body immersed in a liquid experience the greatest pressure? From the top, the sides, or the bottom?
  • What shape does liquid take when it weighs nothing?
  • Why are raindrops round?
  • Can you make a steel needle float?
  • Why does soap wash dirt off?
  • What is thinner? The human hair or the film of a soap bubble?
  • Why does a liquid rise when sipped through a straw?
  • A stick is balanced by weights on a pair of scales. Will the equilibrium be disturbed if the scales are placed under an evacuated bell?
  • What difference is there between a "perpetual motion" machine and a "gift-power" machine? Have any "gift-power" machines been made?
  • Why do lemonade glasses have a thick bottom and why are they no good as tea glasses?
  • Can we make a self-winding clock?
  • Can the self-winding principle be used for bigger machines?
  • Will ice melt sooner if wrapped in fur?
  • Is it true that the snow warms the Earth?
  • Why does a sled cross snow with difficulty in a heavy frost?
  • Why is it warmer at the equator than at the poles?
  • Can we make light circumvent obstacles?
  • Where should you place a lamp to see yourself better in a mirror?
  • Are you and your reflection in a mirror completely identical?
  • How can we use ice to light a fire?

A green ray optical phenomena produced by the sunset or the sunrise.What is the "green ray"? Green flashes, also known as "green rays", are optical phenomena ---not an optical illusion--- produced by the diffraction of the Sun's rays during the sunrise or sunset. It usually lasts for a few seconds, and is visible under very special conditions.
However, Yakov describes in his Physics for Entertainment some rare circumstances under which the green ray effect can be visible for nearly 5 minutes. Photo: Wikipedia.

  • How should one look at photographs?
  • Why do photographs acquire relief and depth when looked at through a magnifying glass or in a concave mirror?
  • Why is it better to look at a painting with one eye?
  • Why do things sparkle?
  • Why does the landscape acquire deeper relief when viewed from a passing train?
  • What is the effect of the so-called "shadow marvel" based on?
  • What color does a red flag assume in blue light?
  • What kind of pictures follow you with their eyes? And why?
  • Are there such things as sound mirrors?
  • Where does sound propagate faster, in air or in water?
  • To what technical uses can echoes be put?
  • Why does a bee buzz?
  • Why is it so hard to spot a chirring grasshopper?
  • What is ventriloquism based upon?

Physics for Entertainment is fully illustrated, with more than 150 illustrations.