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The Brownian ratchet is a thought experiment about an apparent perpetual motion machine postulated by Richard Feynman in a physics lecture at the California Institute of Technology on May 11, 1962 as an illustration of the laws of thermodynamics. In philosophy, physics, and other fields, a thought experiment (from the German Gedankenexperiment) is an attempt to solve a problem using the power of human imagination. ...
This article or section should include material from Parallel Path See also Perpetuum mobile as a musical term Perpetual motion machines (the Latin term perpetuum mobile is not uncommon) are a class of hypothetical machines which would produce useful energy in a way science cannot explain (yet). ...
Richard Phillips Feynman (May 11, 1918 – February 15, 1988) (surname pronounced FINE-man; in IPA) was one of the most influential American physicists of the 20th century, expanding greatly the theory of quantum electrodynamics. ...
A black hole concept drawing by NASA. Physics (from the Greek, φυσικός (physikos), natural, and φÏσις (physis), nature) is the science of the natural world dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces. ...
The California Institute of Technology (commonly referred to as Caltech) is a private, coeducational university located in Pasadena, California, in the United States. ...
May 11 is the 131st day of the year in the Gregorian Calendar (132nd in leap years). ...
1962 (MCMLXII) was a common year starting on Monday (link will take you to calendar). ...
Thermodynamics (from the Greek thermos meaning heat and dynamis meaning power) is a branch of physics that studies the effects of temperature, pressure, and volume changes on physical systems at the macroscopic scale. ...
The device consists of a gear with a ratchet, that vibrates under Brownian motion (hence the name) in a heat bath. The idea is that motion in one direction is allowed by the ratchet, and motion in the opposite direction is prevented. Thus, it might be reasoned, the gear will rotate with a small force continuously in one direction, without any heat gradient. This is against the principle of the second law of thermodynamics, which can be stated as "It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work." A ratchet (a) with a gearwheel (b) In mechanical engineering a ratchet is a device used to restrict motion in one direction. ...
An example of 1000 simulated steps of Brownian motion in two dimensions. ...
A heat bath is a large system that is in thermal contact with some other system of interest. ...
The second law of thermodynamics, in a concise form, states that the total entropy of any thermodynamically isolated system tends to increase over time, approaching a maximum value. // General description In a general sense, the second law says that the differences between systems in contact with each other tend to...
Although the Brownian ratchet seems, at first sight, to extract useful work from Brownian motion, Feynman demonstrated through a number of detailed arguments that its operation would be self-defeating, and would in fact not produce any work. One simplistic way to visualize how the machine might fail is to remember that the ratchet itself will undergo Brownian motion as well. In fact, the ratchet will be a comparable size to the gear and undergo similar size motions. So as often as the machine ratchets forward, it slips due to the ratchet's Brownian motion. However, this idea led to the development of Brownian motors, which do produce useful work, but do not violate the laws of thermodynamics. Brownian motors are nano-scale or molecular devices by which thermally activated processes (chemical reactions) are controlled and used to generate directed motion in space and to do mechanical or electrical work. ...
See also - Brownian motor
- R. D. Astumian (1997). "Thermodynamics and kinetics of a Brownian motor", Science 276, p. 917-922.
Brownian motors are nano-scale or molecular devices by which thermally activated processes (chemical reactions) are controlled and used to generate directed motion in space and to do mechanical or electrical work. ...
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