8/9/2023 0 Comments Simple physics phenomena![]() ![]() ![]() Finally, note that diffusion constants increase with temperature, because average molecular speed increases with temperature. (Each molecule actually collides about 10 10 times per second!). In water, an oxygen molecule moves only about 40μm in 1 s. In water, an oxygen molecule makes many more collisions in its random walk and is slowed considerably. Another interesting point is that D for oxygen in air is much greater than D for oxygen in water. Thus the more massive molecules diffuse more slowly. This decrease is because the average molecular speed at a given temperature is inversely proportional to molecular mass. Note that D gets progressively smaller for more massive molecules. This type of motion is called a random walk. The random thermal motion of a molecule in a fluid in time t. Values of D for various substances, in units of m 2/s. The quantity D is the diffusion constant for the particular molecule in a specific medium. Where x rms stands for the root-mean-square distance and is the statistical average for the process. It can be shown that the average distance x rms that a molecule travels is proportional to the square root of time: The densities of common materials are great enough that molecules cannot travel very far before having a collision that can scatter them in any direction, including straight backward. Fluids, like fish fumes or odors entering ice cubes, can even diffuse through solids.ĭiffusion is a slow process over macroscopic distances. Diffusion is the movement of substances due to random thermal molecular motion. In fluids they move about randomly even in the absence of macroscopic flow. Atoms and molecules are in constant motion at any temperature. Berlin Heidelberg New-York: Springer-Verlag.There is something fishy about the ice cube from your freezer-how did it pick up those food odors? How does soaking a sprained ankle in Epsom salt reduce swelling? The answer to these questions are related to atomic and molecular transport phenomena-another mode of fluid motion. An Open Systems Approach to Quantum Optics. "A new wave equation for a continuous non-demolition measurement". "On unitary evolution and collapse in quantum mechanics". ![]() "Decoherence, the measurement problem, and interpretations of quantum mechanics". ^ B.D'Espagnat, P.Eberhard, W.Schommers, F.Selleri.Quantum Mechanics: Non-Relativistic Theory. | v x ′ − v x | Δ p x ≈ ℏ / Δ t, : CS1 maint: location ( link)). A formula (one-dimensional for simplicity) relating involved quantities, due to Niels Bohr (1928) is given by In particular, a measurement of momentum is non-repeatable in short intervals of time. It is also necessary to distinguish clearly between the measured value of a quantity and the value resulting from the measurement process. It is possible for other, less direct means of measurement to affect the electron. Particle physics Īn electron is detected upon interaction with a photon this interaction will inevitably alter the velocity and momentum of that electron. However, the need for the "observer" to be conscious (versus merely existent, as in a unicellular microorganism) is not supported by scientific research, and has been pointed out as a misconception rooted in a poor understanding of the quantum wave function ψ and the quantum measurement process. Despite the "observer effect" in the double-slit experiment being caused by the presence of an electronic detector, the experiment's results have been interpreted by some to suggest that a conscious mind can directly affect reality. Physicists have found that observation of quantum phenomena by a detector or an instrument can change the measured results of this experiment. This effect can be found in many domains of physics, but can usually be reduced to insignificance by using different instruments or observation techniques.Ī notable example of the observer effect occurs in quantum mechanics, as demonstrated by the double-slit experiment. While the effects of observation are often negligible, the object still experiences a change (leading to the Schrödinger's cat thought experiment). Similarly, seeing non-luminous objects requires light hitting the object to cause it to reflect that light. A common example is checking the pressure in an automobile tire, which causes some of the air to escape, thereby changing the pressure to observe it. This is often the result of utilizing instruments that, by necessity, alter the state of what they measure in some manner. ![]() In physics, the observer effect is the disturbance of an observed system by the act of observation. ![]()
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