Topic: Physics/Fluid Dynamics
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A Feynman sprinkler, also referred to as a Feynman inverse sprinkler or as a reverse sprinkler, is a sprinkler-like device which is submerged in a tank and made to suck in the surrounding fluid. The question of how such a device would turn was the subject of an intense and remarkably long-lived debate.
A regular sprinkler has nozzles arranged at angles on a freely rotating wheel such that when water is pumped out of them, the resulting jets cause the wheel to rotate; both a Catherine wheel and the aeolipile ("Hero's engine") work on the same principle. A "reverse" or "inverse" sprinkler would operate by aspirating the surrounding fluid instead. The problem is now commonly associated with theoretical physicist Richard Feynman, who mentions it in his bestselling memoirs Surely You're Joking, Mr. Feynman! The problem did not originate with Feynman, nor did he publish a solution to it.
- "Feynman sprinkler" | 2017-06-11 | 27 Upvotes 6 Comments
- "Feynman sprinkler" | 2015-06-13 | 42 Upvotes 3 Comments
Fluidics, or fluidic logic, is the use of a fluid to perform analog or digital operations similar to those performed with electronics.
The physical basis of fluidics is pneumatics and hydraulics, based on the theoretical foundation of fluid dynamics. The term fluidics is normally used when devices have no moving parts, so ordinary hydraulic components such as hydraulic cylinders and spool valves are not considered or referred to as fluidic devices.
A jet of fluid can be deflected by a weaker jet striking it at the side. This provides nonlinear amplification, similar to the transistor used in electronic digital logic. It is used mostly in environments where electronic digital logic would be unreliable, as in systems exposed to high levels of electromagnetic interference or ionizing radiation.
Nanotechnology considers fluidics as one of its instruments. In this domain, effects such as fluid-solid and fluid-fluid interface forces are often highly significant. Fluidics have also been used for military applications.
- "Fluidics" | 2018-05-24 | 37 Upvotes 14 Comments
Granular convection, or granular segregation, is a phenomenon where granular material subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection. It is sometimes described as the Brazil nut effect when the largest particles end up on the surface of a granular material containing a mixture of variously sized objects; this derives from the example of a typical container of mixed nuts, where the largest will be Brazil nuts. The phenomenon is also known as the muesli effect since it is seen in packets of breakfast cereal containing particles of different sizes but similar density, such as muesli mix.
Under experimental conditions, granular convection of variously sized particles has been observed forming convection cells similar to fluid motion. The convection of granular flows is becoming a well-understood phenomenon.
- "Granular convection" | 2019-12-10 | 46 Upvotes 22 Comments
A jiggle syphon (or siphon) is the combination of a syphon pipe and a simple priming pump that uses mechanical shaking action to pump enough liquid up the pipe to reach the highest point, and thus start the syphoning action.
- "Jiggle syphon" | 2019-01-27 | 14 Upvotes 2 Comments
The inventor of the SR-71's rules for project management
Clarence Leonard "Kelly" Johnson (February 27, 1910 – December 21, 1990) was an American aeronautical and systems engineer. He is recognized for his contributions to a series of important aircraft designs, most notably the Lockheed U-2 and SR-71 Blackbird. Besides the first production aircraft to exceed Mach 3, he also produced the first fighter capable of Mach 2, the United States' first operational jet fighter, as well as the first fighter to exceed 400 mph, and many other contributions to various aircraft. As a member and first team leader of the Lockheed Skunk Works, Johnson worked for more than four decades and is said to have been an "organizing genius". He played a leading role in the design of over forty aircraft, including several honored with the prestigious Collier Trophy, acquiring a reputation as one of the most talented and prolific aircraft design engineers in the history of aviation. In 2003, as part of its commemoration of the 100th anniversary of the Wright Brothers' flight, Aviation Week & Space Technology ranked Johnson eighth on its list of the top 100 "most important, most interesting, and most influential people" in the first century of aerospace. Hall Hibbard, Johnson's Lockheed boss, referring to Johnson's Swedish ancestry, once remarked to Ben Rich: "That damned Swede can actually see air."
- "The inventor of the SR-71's rules for project management" | 2014-12-18 | 126 Upvotes 56 Comments
Pitch Drop Experiment
The pitch drop experiment is a long-term experiment which measures the flow of a piece of pitch over many years. 'Pitch' is the name for any of a number of highly viscous liquids which appear solid; most commonly bitumen. At room temperature, tar pitch flows at a very low rate, taking several years to form a single drop.
- "Pitch Drop Experiment" | 2020-02-06 | 97 Upvotes 30 Comments
Salter's duck, also known as the nodding duck or by its official name the Edinburgh duck, is a device that converts wave power into electricity. The wave impact induces rotation of gyroscopes located inside a pear-shaped "duck", and an electrical generator converts this rotation into electricity with an overall efficiency of up to 90%. The Salter's duck was invented by Stephen Salter in response to the oil shortage in the 1970s and was one of the earliest generator designs proposed to the Wave Energy programme in the United Kingdom. The funding for the project was cut off in the early 1980s after oil prices rebounded and the UK government moved away from alternative energy sources. As of May 2018 no wave-power devices have ever gone into large-scale production.
- "Salters Duck" | 2015-01-30 | 84 Upvotes 39 Comments
Tea leaf paradox
The tea leaf paradox is a phenomenon where tea leaves in a cup of tea migrate to the center and bottom of the cup after being stirred rather than being forced to the edges of the cup, as would be expected in a spiral centrifuge. The correct physical explanation of the paradox was for the first time given by James Thomson in 1857. He correctly connected the appearance of secondary flow (in both Earth atmosphere and tea cup) with ″friction on the bottom″. The formation of secondary flows in an annular channel was theoretically treated by Boussinesq as early as in 1868. The migration of near-bottom particles in river-bend flows was experimentally investigated by A. Ya. Milovich in 1913. The solution first came from Albert Einstein in a 1926 paper in which he explained the erosion of river banks, and repudiated Baer's law.