Closed encounters of the fourth kind

Classical Mechanics Level 1

Open systems are systems in which both matter and energy can pass in and out of freely. Closed systems are systems where energy but not matter can pass through. Finally, isolated systems are systems wherein neither energy nor matter can enter.

Can there exist a fourth system, where only matter but not energy can pass through?

Yes No

Jake Lai by Jake Lai , 21, Singapore

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2 solutions

Jake Lai
Jul 18, 2015

There will always be transfer of energy in the form of thermal, kinetic, or chemical/gravitational/elastic potential energy (along with a whole slew of other types) whenever any matter enters a system.

Even if one only considers elementary particles (without KE/CPE/EPE/GPE/etc), even then there is still transfer of thermal energy by convection due to the third law of thermodynamics.

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What about an ideal heat exchanger, which would be an example of a Closed System where matter passes through but not energy? That's what heat exchangers are for, which is to take the energy out of one mass stream and put it into another. The net energy flow through the boundary is zero.

And then if we're allowed to consider conversion of energy into matter, well, we can take the example of a Closed System whereby only energy leaves the system, but we convert that energy into matter, which then leaves the meta-system. Thus, we'd have created the second kind of Closed System.

The examples given in this problem, Open, Closed, and Isolated, are those in practical use in physics of Thermodynamics. It would be a bad idea to imagine that only they hold in all aspects of physics.

Michael Mendrin - 5 years, 10 months ago

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Ideal heat exchanger do change energy, it's indeed its main purpose. it does so with the least possible leakage and with the highest efficiency, but it remains a process by which energy is passed from one place to another (with possible conversions).

You can't imagine a system where energy passes and hence imagine that mass passed as well, heat is not mass for instance. But one can imagine a nuclear reaction where the inverse process of fission would happen (although, I don't think it is feasible, it may be thought experiment): you make a fission reaction on a Uranium atom: energy leaves the system and goes into another system made of the product of the reaction and the energy reminds them. In that case, the flow from one system to the next was purely of energy, then that energy was used to create mass.

Benjamin Katz-Crowther - 5 years, 10 months ago

All matter has energy.

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