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. These tiny engines operate in an environment where viscosity dominates inertia, and where thermal noise makes moving in a specific direction as difficult as walking in a hurricane: the forces impelling these motors in the desired direction are minuscule in comparison with the random forces exerted by the environment. The Pitch Drop Experiment at the University of Queensland. ... Inertia is the tendency of any state of affairs to persist in the absence of external influences. ... Johnson-Nyquist noise (sometimes thermal noise, Johnson noise or Nyquist noise) is the noise generated by the equilibrium fluctuations of the electric current inside an electrical conductor, which happens without any applied voltage, due to the random thermal motion of the charge carriers (the electrons). ...
In biology, many protein-based molecular motors in the cell may in fact be Brownian motors. These molecular motors convert the chemical energy present in ATP into mechanical energy. One example of a Brownian motor would be an ATPase motor that hydrolyzes ATP to generate fluctuating anisotropic energetic potentials. The anisotropic potentials along the path would bias the motion of a particle (like an ion or polypeptide); the result would essentially be diffusion of a particle whose net motion is strongly biased in one direction. The translocation of the particle would only be loosely coupled to hydrolysis of ATP. Because this type of motor is so strongly dependent on random thermal noise, it is likely that Brownian motors are feasible only at the nanometer scale.
The dynamics and activity of Brownian motors are current fields of study in theoretical and experimental biophysics. Many researchers are presently engaged in understanding how molecular-scale motors operate in environments with non-negligible thermal noise. Biophysics (also biological physics) is an interdisciplinary science that applies theories and methods of the physical sciences to questions of biology. ...
Brownianmotors 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.
The dynamics and activity of Brownianmotors are current topics of study in theoretical and experimental biophysics.
Brownianmotors are sometimes modeled using the Fokker-Planck equation or with Monte Carlo methods.
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.
The device consists of a gear with a ratchet, that vibrates under Brownian motion (hence the name) in a heat bath.
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.
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