Jumping stones
The skipping stones (for other names see the section on synonyms ) is a pastime in which it applies, a flat stone to throw so that it as often as possible over a water surface jumps before it sinks.
Synonyms
There are numerous slang or regional names for jumping stones over the water. As early as 1816, Friedrich Ludwig Jahn listed a number of synonyms:
"In all water areas, the Schirken is an amuse the child, and has on the individual dialects in landscapes and districts different names: bämmeln solve the peasant, leaden, lead the bride, cut bread, emphasize Butterbämmen, lubricate sandwich, ~ throw, butter stollen throwing, fishing, flattening, flattening - also flattening - throwing, flötzen, flözern, throwing frogs, heating up, shooting maidens, ~ throwing [,] - a one-two- or three-legged maid, throwing a child, loosing the dear woman, grooming, plowing, splashing, flattening, puttying, making boats [,] ~ beating, shuffling, sailing, beating faster, faster, throwing bowls, spätzeln, pricking starlings, making Steinblitzer, stone, stilting, making soup [,] ~ throwing [,] ~ melt. "
About three decades earlier, an anonymous author saw butterstullen throwing as the "common" expression and still referred to the synonym frog loosing . Hermann Wagner's playbook for boys (1864) only speaks of throwing stones . The designation to lead the bride is already documented in 1616.
Other synonyms or phonetic variants of the terms mentioned in the quote from Jahn / Eiselen are Ditschen , Schnellen / Schnellern (meaning "move quickly with spring force"), Pfitscheln , Flitschen , Fitscheln (Saxony, Thuringia), in Austrian Flacherln or Blattln , in Swiss German Schiferen or Bämmelen .
history
During the Roman Empire , Minucius Felix described in his dialogue Octavius how children play this game on the beach. Even Julius Pollux documented the game in his onomasticon . In 1585 John Higgins mentioned in his translation of Hadrianus Junius ' Lexicon Nomenclator that oyster shells were used in addition to stones. Eskimos and the Bedouins also know the game and use ice or sand as a surface.
World record holder in the Guinness Book of Records has been Kurt Steiner since September 2013 with 88 jumps, bridging a distance of almost 100 meters.
Scientific aspects
Physical basics
For the perfect execution of the stone hopping, some physical conditions have to be met. The stone must be in the shape of a flat ellipsoid or disk and must be thrown so that the flattened side and the surface of the water form an angle between 0 ° and 45 °. The dropping height should be as deep as possible, preferably not much higher than the surface of the water itself. Calm water with few waves and as little cross wind as possible is also necessary. In addition, the stone must be set in rotation about its vertical axis. This behavior is known from gyroscopes : As long as there is no torque affecting the movement , the rotation remains unchanged and stabilizes the missile. If you throw stones without this additional angular momentum , they lose their alignment due to small disturbances during the flight. When they hit the water, they submerge. A self-rotating movement of the stone can be achieved by holding the stone between the thumb and middle finger and applying pressure with the index finger on the edge of the stone at the moment of throwing it off. Larger stones are held between the thumb and middle finger and the index finger is placed on the narrow side, where it generates the rotation when thrown by tangential force.
As soon as the stone hits the surface of the water, however, it does not spring back like a ball, as might initially be assumed, because the surface of the water does not look like a solid body. That is why it is amazing that a stone can jump on water at all. Film recordings show that the stone thrown at an acute angle to the surface of the water hits the water with its rear edge first. The stone then, stabilized by its turning movement, first glides a little bit on the surface of the water and pushes a small wall of water in front of it like a bow wave , which it catches up with at sufficient speed : like on a ski jump , it glides up this wave and goes to the next jump. Due to friction losses , it loses kinetic and rotational energy with every contact with the water surface. The jumps become increasingly shorter and then turn into a kind of slide. After all, either the speed of the stone is so low that it can no longer catch up with the bow wave and sinks into the water, or its twist is no longer sufficient - this is especially the case with small stones - to stabilize its path. The stone then no longer hits the water flat and submerges.
Application in military technology
During the Second World War , roll bombs were used to destroy German dam walls. These were set in rotation and thrown from the aircraft at high speed low-altitude. As a result, they bounced off the surface of the water several times, analogous to the stones when jumping stones. In this way, the defense nets in the water, which prevented the use of torpedoes, could be bypassed.
Scientific investigations
The researchers Lionel Rosellini, Christophe Clanet, Fabien Hersen and Lydéric Bocquet from the Universities of Marseille and Lyon have experimentally investigated the conditions for the optimal stone throw. They constructed a throwing machine that hurled aluminum disks as flat model stones onto a surface of water. During the throws, the scientists varied the speed at which the stone was thrown, its angle of impact on the water and the rotation of the disc itself. The sequence of movements was documented with a high-speed camera . When evaluating the data, the scientists came to the conclusion that short contact times with the water surface have a decisive influence on the number of possible jumps: the shorter the contact, the less energy is lost through friction. In the experiment, this time was less than 10 ms. The energy losses are also the reason why stones with low initial speeds are not very successful. Regardless of the natural rotation or the speed of the stone, the optimal contact time was reached when the stone hit the water surface at an angle of 20 °. At impact angles over 45 °, the jump phenomenon could no longer be observed at all. Stone jumps can also be performed on damp sand . It can be observed that short and long jump distances alternate. Film recordings show that the short gaps arise when the back and front edges of the stone meet the sand, which is more solid than the water. The stone is slowed down by the impact so that it tips over before it starts to jump again.
Comparison with re-entry into the atmosphere (space travel)
The bouncing effect of the stones is also used as an explanation for the “bouncing” of a spacecraft when it re- enters the earth's atmosphere too shallowly . However, this is wrong, usual re-entry bodies generate too little lift for this. The supposed "bounce" is a geometrical effect: If the brakes are too little, the path remains approximately an ellipse, on which the body first approaches the planet (see proximity to earth or perigee ) and later away again. If this orbit is interpreted as the height above the planet's surface, there is initially a decrease and later an increase again. Even multiple immersion in the atmosphere during atmospheric braking shows a picture similar to the jumping stone with a simple plot of the orbit height, but has a completely different cause. Space gliders with a much stronger buoyancy, such as the Silbervogel or the Waverider, would make it possible to hop similar to a stone in the high atmosphere, but they are still a long way off.
literature
- August Mau : Ἐποστρακισμός . In: Paulys Realencyclopadie der classischen Antiquity Science (RE). Volume VI, 1, Stuttgart 1907, Col. 251.
- CL Stong: In: Scientific American . Volume 219, 1968, p. 112
- J. Trefil: Physics in a beach chair . Rowohlt Verlag Hamburg 1991
- Lydéric Bocquet: The physics of stone skipping . In: American Journal of Physics . tape 71 , no. 2 , 2003, p. 150–155 , doi : 10.1119 / 1.1519232 , arxiv : physics / 0210015 , bibcode : 2003AmJPh..71..150B (English).
- Christophe Clanet, Fabien Hersen, Lydéric Bocquet: Secrets of successful stone-skipping . In: Nature . tape 427 , 2004, pp. 29 , doi : 10.1038 / 427029a (English, researchgate.net ).
- Lionel Rosellini, Christophe Clanet, Fabien Hersen, Lydéric Bocquet: Skipping Stones . In: Journal of Fluid Mechanics . tape 543 , 2005, pp. 137-146 , doi : 10.1017 / S0022112005006373 (English, researchgate.net ).
Web links
- Video of Kurt Steiner's world record in jumping stones from September 2013 on YouTube , accessed on December 7, 2019.
Individual evidence
- ^ Friedrich Ludwig Jahn: The German art of gymnastics for the establishment of the gymnastics fields. Berlin 1816. pp. 125-126. Digitized
- ↑ Anon. [P.]: To the PB in C. In: Very newest manifolds. A non-profit weekly journal, Volume 3 (1784), 49th week, pp. 795f. Digitized
- ^ Hermann Wagner: Illustrated playbook for boys. 1001 entertaining and stimulating amusements, games and activities for body and mind, outdoors and in the room. 2. unchangeable Ed. Leipzig: Spamer 1864, p. 116 (No. 331). Digitized
- ^ Georg Henisch: Teutsche Sprach und Weißheit. Thesaurus linguae et sapientiae Germanicae. Auguste Vindelicorum 1616, p. 486. Digitized
- ↑ ' Schnell ' in the South Hessian dictionary; 'Speed up' in the Rhenish dictionary
- ↑ Johann Christoph Adelung : Grammatical-critical dictionary of the High German dialect . 2nd Edition. Johann Gottlob Immanuel Breitkopf and Compagnie , Leipzig 1793 ( zeno.org [accessed on January 30, 2020] dictionary entry “Schnellen”).
- ↑ 'flitschen' in the Palatinate dictionary
- ↑ Sachsen Welt - Saxon dictionary and dialect. Accessed January 30, 2020 .
- ↑ Schweizerisches Idiotikon , Vol. 8, Col. 379
- ↑ Schweizerisches Idiotikon , Vol. 4, Col. 1229
- ↑ Marcus Minucius Felix: Octavius (cap. 3). Latin , English
- ^ Wilhelm Dindorf (Ed.): Julii Pollucis Onomasticon. Leipzig 1824, archive.org, p. 191 (section 9.119)
- ↑ entry "Epostracismus" in Nomenclator 1585, page 299
- ↑ Guinness World Records: Most skips of a skimming stone , accessed March 31, 2016
- ↑ H. Joachim Schlichting: Hop, stone, hop! In: spectrum. March 23, 2016, accessed November 16, 2019.
