In what liquid can a coin float and a cork sink? Detailed answer

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In what liquid can a coin float and a cork sink? Detailed answer

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In what liquid can a coin float and a cork sink?

Such liquids are called ferromagnetic, or ferrofluids. They are a colloidal system based on a liquid (for example, water, kerosene or oil), in which the smallest particles of a solid ferromagnet (for example, iron or nickel) are “dissolved”.

The resulting dispersion medium "behaves" like a liquid with magnetic properties. By applying a vertically directed constant magnetic field to it, it is possible to change the magnitude of the buoyant (Archimedean) force acting on a body immersed in a ferrofluid.

If the vector of the magnetic field strength is directed downwards, then the magnetic force generated in this fluid will add up to the gravitational force (gravity) and the ferrofluid will behave as if its density has increased. As soon as the magnetic field strength reaches a sufficiently high value, the copper coin lying at the bottom of the vessel will float, as if it were in a liquid whose density is higher than that of copper.

If the magnetic field strength vector is directed upwards, then the magnetic force generated in the fluid will reduce the effect of gravity, and the ferrofluid will behave as if its density has decreased. When the magnetic field strength reaches a certain value, at which the magnetic force in the liquid almost becomes equal to the force of gravity (the ferrofluid becomes almost "weightless"), the cork floating on the surface will sink.

Author: Kondrashov A.P.

Random interesting fact from the Great Encyclopedia:

To whom were defenders provided in court and who did not receive them in accordance with the Decree on the reorganization of the Revolutionary Tribunal adopted by the Convention on June 10, 1794 (22 Prairial of the XNUMXnd year of the Republic)?

In this decree, adopted with the aim of "guaranteeing the freedom of slandered patriots" and speeding up the trial of "conspirators", it was proclaimed: "The law provides slandered patriots as defenders of sworn patriots; it does not provide them to the conspirators." Thus, the question of guilt was decided before the trial.

The law was adopted on the report of Couthon and with the support of Robespierre, who in two of his speeches insistently demanded its immediate implementation. At the same time, Robespierre did not hesitate to declare that in this law "there is not a single article that would not be based on justice and reason."

As a result of the application of this law, from June 10 (22 Prairial) to July 27 (9 Thermidor), 1794, 1351 people died in Paris alone.

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Clay XNUMXD Printing 27.05.2009

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Three-dimensional printing, that is, the production of three-dimensional objects from a computer model using a special printer, is a very interesting technology. Today it is used not only for designing machine parts or making individual prostheses: sculptors and museum workers have also begun to be interested in the possibility of creating small editions of works of art.

As a result, there are more and more students who come to learn how to work with such equipment. This means that the need for consumables is increasing, and they are expensive.

“We are now spending up to $4000 a quarter to buy branded clay for such a printer. This is too much for our budget. In fifteen years of operation, we have spent so much money on consumables that the initial cost of a printer - $ 20 - seems now just ridiculous " says Mark Gunter of the University of Washington.

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