Carrock
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Posts posted by Carrock
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test
in The Sandbox
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37 minutes ago, Ghideon said:4 hours ago, Carrock said:
As LIGO is able to detect gravitational waves, some energy has to be taken from those waves.
I think I agree on that, and I would like to understand more about how that works. When trying to formulate some analogy my attempts sounds too vague and opens for possibilities that the gravitational wave could be unaffected. Like: I could measure the distance of one meter without affecting "the meter", space time coordinates are unaffected by my activities*. Or: I could measure and calculate time dilation without affecting the passing of time?
Your comment is spot on regarding my question; are there (tiny) effects on gravitational waves passing trough matter, effects that are not there when the wave passes through vacuum.
LIGO's detection proves the GW energy is there; the GW energy would still there even without LIGO detecting it so any LIGO measurement effect is not really an issue.
The mutual coupling between gravitational waves and the earth is so weak that the energy required to stretch or compress matter is (very very very) nearly entirely lost from the gravitational waves.
I think there are no analogous effects when the wave passes through vacuum.
I've gone well beyond my minimal knowledge of gravitational waves; regard the above as plausible speculation.
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As LIGO is able to detect gravitational waves, some energy has to be taken from those waves.
As electromagnetic radiation from some of the sources is comparatively extremely easy to detect, the energy absorbed by even the whole earth would be very small, with no detectable effect on the gravitational waves.
Some of the comments after https://stuver.blogspot.com/2012/07/journey-of-gravitational-wave-i-gws.html look at different ways energy could be absorbed.
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3 hours ago, studiot said:
All states are "equilibrium states".
A condition of non equilibrium is not defined/definable.
This arises because the full description of a state comprises a list of the values of all state variables, each of which which must by definition represent the entire system.
I don't agree with part or all of this but I suppose I can see its relevance for the following post.
1 hour ago, studiot said:What about the work done in the expansion?
"No work has been done"
Well look at this....
I tried to indicate I was only concerned with initial and final conditions in my example of how an isolated system can increase its entropy from one well defined value to another well defined value. The total work done in getting from the low entropy state to the final high entropy state, which is an "equilibrium state" where the entire volume y (or A plus B) is in equilibrium, is zero.
While transitioning between states work is done.
2 hours ago, studiot said:Now any further expansion will be against this (albeit small) positive pressure so work must be done.
Also the temperature of the gas is lowered and it acquires kinetic energy.
As the volume y comes to equilibrium all this work is transformed to heat.
At equilibrium the temperature of the gas in the volume y is the same as it was in x.
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I thank you also Timo.
I reread this thread in light of your post and saw a comment I missed and should have addressed.
On 5/19/2019 at 12:11 PM, studiot said:In order to calculate the entropy change for an irreversible path we must find an alternative reversible method of going from state A to state B and then use this to calculate the entropy change.
I disagree with 'must.'
It is IMO a very good calculation method. I don't think its impossibility re my isolated system would prevent its use with the working assumption that my system is temporarily not isolated. But it's not the only method.
Save mouse wheel....
On 5/19/2019 at 3:50 PM, Carrock said:You cover "in an isolated system entropy need not increase."
I'll assume ideal, classical conditions, including an ideal gas.
An (old) example of "in some isolated systems entropy can increase:"
You have an x cubic units sealed container of ideal gas, inside an empty sealed container of y cubic units.
A side of the smaller container is 'instantaneously' removed without otherwise affecting the system.
The gas irreversibly expands and comes to equilibrium in the y cubic units container. No work has been done so the temperature has not changed.
The entropy has increased by the factor ln(y/x).
I used this example for simple maths.
The crucial issues.
6 hours ago, timo said:If one insists on calling the two systems a single, unified system right after contact, then this unified system is not in an equilibrium state (**). And I believe this is exactly where your disagreement lies: Does this unified, non-equilibrated state have an entropy? I do not know. I am tempted to go with studiot and say that entropy in the strict sense is a state variable of thermal equilibrium states - just from a gut feeling.
The gas in x and the empty rest of y are each in equilibrium states until the first atom leaves the x volume. I believe the entropy of the entire system can be calculated when each part is in self equilibrium.
The following seems to confirm that view.
7 hours ago, timo said:In the theory of thermodynamic processes, both systems' states change to the final state through a series of individual equilibrium states (*). Because of their different temperatures and conservation of energy (and because/if the higher-temperature system is the one losing heat to the colder) the sum of entropies increases.
After the side is removed but before any atom has passed the position of the missing side calculate the entropy of the gas still in equilibrium in the volume x. See e.g. http://hyperphysics.phy-astr.gsu.edu/hbase/Therm/entropgas.html (latexphobia.). The entropy of the empty part of y is 0.
The subsequent expansion is not isothermal but the final equilibrium temperature of the gas is the same as before it expanded.
The new entropy of the gas in volume y can be calculated.(latexphobia.)
Entropy change:
delta S = nK ln(y/x)
The important difference between my and timo's examples is that in mine there is equilibrium only in the initial and final states and there are always equilibrium states in his.
IMO this isn't a problem...
3 hours ago, studiot said:.... Thermo can get quite tricky when you start to think deeply about it.
Definitely agree.
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2 hours ago, studiot said:
I meant (and said) that the irreversible process has changed the system. So the state of the new system (being a list of values of all state variables) differs from that of the original system.
When you change a system how does that become a new system rather than a modified system? You seem not to be distinguishing between a system and its state. This is unconventional and confusing.
- Would you disagree with "So the modified state of the system (being a list of values of all state variables) differs from the original state of the system?"
2 hours ago, studiot said:So it can truly be said that a system in state A can be taken to state B and returned to state A as the same system, but with changes in the surroundings.
It is the emboldened phrase that is the usual way of putting this, but that is all too often ignored.
I specified an isolated system with entropy increasing so that these and some other issues would be irrelevant.
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11 hours ago, studiot said:
Have you heard of the equipartition theorem?
Yes. From a brief look the reference you gave is clear and accurate.
In it 'temperature' is frequently used but not derived. e.g.
QuoteThe equipartition theorem can go further than simply predicting that the available energy will be shared evenly amongst the accessible modes of motion, and can make quantitative predictions about how much energy will appear in each degree of freedom. Specifically, it states that each quadratic degree of freedom will, on average, possess an energy 1⁄2kT.
So this version, probably edited/simplified for students, of the equipartition theorem can't be used in a definition of temperature. I hope this response is relevant.
1 hour ago, swansont said:Bodies are in equilibrium with other bodies, not with themselves.
You don't have to assume that heat flows in a particular way. The only requirement is that no heat is flowing.
Heat could flow from cold to hot and the law still works because the law is not about the details of heat flow. It is merely to define the transitive property of equilibrium (i.e. it's about temperature, not heat)
I don't doubt that you're right and I'm wrong, not least from your work on clocks. Understanding how you're right is still an issue for me.
Thanks for your help and patience; I've now reached a point where I have to do some actual reading.
I'm now rather dubious about reader friendly Wikipedia, so I'm going to have to look for relevant peer reviewed papers, or at least preprints.
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5 minutes ago, studiot said:
It's more important and more subtle than that.
Really?
7 minutes ago, studiot said:Your proposed experiment uses an irreversible process.
This means that since the original system is isolated and remains so it cannot interact with its surroundings.
The second sentence is true whether or not the process is irreversible.
11 minutes ago, studiot said:But the only way to restore the system to its original state is by way of an external intervention or interaction.
Entropy has been increased so of course.
44 minutes ago, studiot said:In truth the original state is not accessible to the new system after the irreversible process.
Did you mean: the original state of the isolated system cannot be restored after the irreversible process has changed the state of the system?
Entropy has been increased so of course.
16 minutes ago, studiot said:In truth the original state is not accessible to the new system after the irreversible process.
This is because there are really two systems the original system and the new or transformed system.
The state of either of these systems is inaccessible to the other.
Clarify please. I don't see any sense in the second or third sentence.
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4 hours ago, studiot said:
For what it's worth, my understanding of the Zeroth law is that it introduces the three important equivalence relations into thermodynamics thus:
Consider 3 separate thermodynamic systems, Z1, Z2,and Z3 (we use Z to avoid confucion with entropy)
1) Then if Z1is in equilibrium with Z2 and Z3 is also in equilibrium with Z3 then Z1 is in equilibrium with Z3 ( This is the transitive property).
2) Z1 is in equilibrium with itself (reflexive property).
2) Z1 in equilibrium with Z2 implies Z2 is in equilibrium with Z1 (symmetric property).
These assertions can be used to show that thermodynamic temperature is a property of a system and was originally proposed by Maxwell under the title the Law of Equal temperatures (1872)
I agree with your post with caveats - see below.
I've been looking through Wikipedia and it doesn't exactly help.
My problem is how do you tell if e.g. Z1 is in equilibrium with itself and with Z2 without assuming heat flows from hot to cold? An answer seems to be that if Z1 and Z2 are in contact for a long time without changing they are in equilibrium.
From https://en.wikipedia.org/wiki/Zeroth_law_of_thermodynamics
QuoteThe zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third one, then they are in thermal equilibrium with each other. Accordingly, thermal equilibrium between systems is a transitive relation.
Two systems are said to be in the relation of thermal equilibrium if they are linked by a wall permeable only to heat and they do not change over time.
But if heat doesn't flow from hot to cold (or from cold to hot) they presumably wouldn't change from whatever weird states they were in i.e. mutual equilibrium would be a meaningless concept. So heat flows from hot to cold seems to be a necessary postulate for the zeroth law....
And from https://en.wikipedia.org/wiki/Temperature#Zeroth_law_of_thermodynamics
QuoteZeroth law of thermodynamics
Main article: Zeroth law of thermodynamicsWhen two otherwise isolated bodies are connected together by a rigid physical path impermeable to matter, there is spontaneous transfer of energy as heat from the hotter to the colder of them. Eventually, they reach a state of mutual thermal equilibrium, in which heat transfer has ceased, and the bodies' respective state variables have settled to become unchanging.
One statement of the zeroth law of thermodynamics is that if two systems are each in thermal equilibrium with a third system, then they are also in thermal equilibrium with each other.
Heat flows from hot to cold assumed.....
More Wikipedia : Heat flows from hot to cold is three laws down from the second law?!
From https://en.wikipedia.org/wiki/Thermal_equilibrium#Internal_thermal_equilibrium_of_an_isolated_body
QuoteOne may imagine an isolated system, initially not in its own state of internal thermal equilibrium. It could be subjected to a fictive thermodynamic operation of partition into two subsystems separated by nothing, no wall. One could then consider the possibility of transfers of energy as heat between the two subsystems. A long time after the fictive partition operation, the two subsystems will reach a practically stationary state, and so be in the relation of thermal equilibrium with each other. Such an adventure could be conducted in indefinitely many ways, with different fictive partitions. All of them will result in subsystems that could be shown to be in thermal equilibrium with each other, testing subsystems from different partitions. For this reason, an isolated system, initially not its own state of internal thermal equilibrium, but left for a long time, practically always will reach a final state which may be regarded as one of internal thermal equilibrium. Such a final state is one of spatial uniformity or homogeneity of temperature.[4] The existence of such states is a basic postulate of classical thermodynamics.[5][6] This postulate is sometimes, but not often, called the minus first law of thermodynamics.
Wikipedia is usually reliable but all I can really say is that my knowledge of what I don't know about thermodynamics has significantly increased.
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5 hours ago, studiot said:
Yes, it's true that if you physically change the system, the new system can have greater entropy than the original.
The original system can never gain entropy if isolated.
Maybe a misunderstanding? If the original system is in equilibrium, then it can never gain entropy if isolated.
In my example the side of the small box was removed 'instantaneously,' taken out of the larger box and the larger box sealed 'instantaneously,' before any ideal gas atoms could escape. That was the original isolated system, which then spontaneously changed itself and increased its entropy.5 hours ago, studiot said:Do you understand why this is and that this is why the old formulations were made in terms of cyclic processes?
No and yes.
Rather than pretend I didn't refresh my understanding, I'll just quote a bit of Wikipedia e.g.:
https://en.wikipedia.org/wiki/Thermodynamic_cycle#Modeling_real_systems
QuoteThe repeating nature of the process path allows for continuous operation, making the cycle an important concept in thermodynamics.
The value of this concept can often be seen during problematic, non cyclic engine startup, before the startup transients die down.
Enough for today!
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1 hour ago, John Cuthber said:
I wonder if anyone has ever set up a chain of frequency multipliers (doublers or whatever) to convert the very accurate 60 KHz signal used by radio controlled clocks up to something in the MHz region for calibration/ checking of frequency meters.
You can get multipliers designed for this but they are PLL based.A sequence of accurate 60, 120, 180... KHz test frequencies might be useful.
A trippler gives you 180 KHz and a quintupler gives you 300 KHz
Any thoughts?
Most (digital) frequency meters can also be configured to measure time. A divide by 60,000 or more device would at least be simpler than a multiplier. Noise and jitter in the MSF signal would be a problem; a very large division ratio would reduce those but maybe not enough.
Getting high accuracy is the big issue whatever you do.
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2 minutes ago, swansont said:
The zeroth law doesn’t address how you get to equilibrium. Doesn’t address heat transfer at all.
No, it assumes (parts of) the second law etc. The idea of the zeroth law being more fundamental than the second law while relying on concepts like equilibrium from the second law is what I find problematic.
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44 minutes ago, swansont said:
You made that clear. I gave a more rigorous description
Heat associated with warm water? Heat is energy transfer.
I agree... I did not expect to find this definition of heat.
QuoteFor the precise definition of heat, it is necessary that it occur by a path that does not include transfer of matter.[12]
So heat can't flow from cold to hot. Got it.
12 hours ago, Carrock said:I was basically objecting as politely as I could to studiot's second law, which is a duplicate of part of the zeroth law.
1 hour ago, swansont said:No, it’s not.
According to all the references I could find I'm wrong here as well, but I can't see why.
e.g. from https://en.wikipedia.org/wiki/Zeroth_law_of_thermodynamics
QuoteThe zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third one, then they are in thermal equilibrium with each other. Accordingly, thermal equilibrium between systems is a transitive relation.
How can any system be in thermal equilibrium, or be measured to be in thermal equilibrium with another system unless 'heat flows from hot to cold' is part of the zeroth law? Alternatively, 'heat flows from hot to cold' could be part of both laws, but that is messy at best.
If (plausibly) the second law cannot be formulated without some version of the zeroth law then the zeroth law should surely not rely on part of the second law.
As my thermodynamics is (obviously) rusty, I expect I've overlooked something obvious.
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1 hour ago, studiot said:
This thread was inspired by the following comment in this query about air conditioning.
QuoteCarrock :2nd law: In an isolated system entropy will increase or remain the same.
But is that so ?
The change in entropy going from state A to state B is always the same, irrespective of the path between A and B since entropy is a state variable and thus a function of the state of the system alone.
It make no difference whether that path is reversible or irreversible.
...............................
For any completely isolated system we are restricted to adiabatic processes since no heat can either enter or leave the sytem.
For a reversible process in any such system dq=0, hence ΔS is also zero, which means that S is a constant.
Thus if one part of the system increases in entropy another part must decrease by the same amount.
You cover "in an isolated system entropy need not increase."
I'll assume ideal, classical conditions, including an ideal gas.
An (old) example of "in some isolated systems entropy can increase:"
You have an x cubic units sealed container of ideal gas, inside an empty sealed container of y cubic units.
A side of the smaller container is 'instantaneously' removed without otherwise affecting the system.
The gas irreversibly expands and comes to equilibrium in the y cubic units container. No work has been done so the temperature has not changed.
The entropy has increased by the factor ln(y/x).
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1 hour ago, swansont said:
Heat doesn’t spontaneously flow from cold to hot.
I don't regard "of its own accord" as very scientific...
From my water example, does the heat associated with warm water molecules not accompany those molecules spontaneously/of its own accord when they become vapour? I would regard your statement as entirely accurate for systems referred to in the zeroth law.
I was basically objecting as politely as I could to studiot's second law, which is a duplicate of part of the zeroth law.
6 hours ago, studiot said:The zeroth laws says that to transfer heat you must have a temperature difference.
The second law says that heat will not flow of its own accord from a colder body to a warmer one.
The zeroth law involves thermal equilibrium and is needed to define temperature.
It's impossible (I think) to have stable thermal equilibrium without the explicit/implicit assumption or law that heat flows from hot to cold in the systems relevant to the zeroth law.
3 hours ago, studiot said:Note the word I missed out was continuously so "heat will not flow continuously from a colder body to a warmer one" is more accurate.
Why bring entropy into it at all?
"heat will not flow continuously from a warmer body to a colder one" is also accurate.
Both are non equilibrium systems. I am assuming they are finite.
I brought entropy into it because because I thought you gave a hasty, inaccurate version of the second law.
It is very easy to get tripped up by all the ifs and buts in thermo.
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1 hour ago, studiot said:
The zeroth laws says that to transfer heat you must have a temperature difference.
The second law says that heat will not flow of its own accord from a colder body to a warmer one.
And, of course, your walls are warmer than the air you are trying to cool.
Maybe oversimplified, therefor misleading? Particularly "of its own accord" - rather anthropomorphic.
alternative:
Zeroth law: If two systems are isolated except for a heat permeable wall then heat will flow from hot system to cold system. (If the two systems do not change over time and there is no net heat flow they are at the same temperature.)
2nd law: In an isolated system entropy will increase or remain the same.
Heat can flow from cold to hot provided total entropy does not decrease. An example is water evaporating into air at the same initial temperature. The higher energy water molecules leave preferentially, lowering the temperature of the remaining water and warming the air.
(Intended to complement earlier posts.)
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38 minutes ago, Conjurer said:
In the transceiver of a radar, wave-guides are used that are at half wave lengths and full wavelengths, so the transmitter does not burn out the transceiver. It does this by making wave-guides a half wavelength to the receiver. Then the only waves that enter the receiver are the ones that are reflected from outside of the antenna. Then the same piece of wave-guide can be used while only using one single antenna.
Nope.
Wave guides are not one way guides of R.F. energy.
You're thinking of circulators, which rely on permanent magnets.
QuoteFerrite circulators are often used as a duplexer. The operation of a circulator can be compared to a revolving door with three entrances and one mandatory rotating sense. This rotation is based on the interaction of the electromagnetic wave with magnetised ferrite. A microwave signal entering via one specific entrance follows the prescribed rotating sense and has to leave the circulator via the next exit. Energy from the transmitter rotates anticlockwise to the antenna port. Virtually all circulators used in radar applications contain ferrite.
At first in Ferrite circulators the energy divides into two equal parts at the entrance (1), but these parts get a different propagation speed by the influence of the ferrite.
edit or using half wave transformers etc to interface with spark gaps etc used for switching.
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21 minutes ago, Sensei said:
Are not you talking about multiple sources, on multiple machines ("servers" or "peers"), single target user.. ?
Sort of.
First user starts downloading from source server.
Second user gets partial downloads from source server and from first user, who has already downloaded part of file.
Third user downloads from source, first and second users. First user can now download from source, second and third users. And so on...
My post was only a response to the OP's second sentence.
11 hours ago, fiveworlds said:Is there an existing application/hardware that will allow a single computer to send duplicate network traffic to multiple computers. For example, say I want many computers to download the same update file?
i.e. I felt his first sentence unnecessarily limited his options.
Sensei: "Torrent is rather not an option, if you want to redistribute your own legit software, to worldwide clients."
BitTorrent is an option for every major Linux OS worldwide download; users are requested to download with BitTorrent or similar to reduce server load.
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11 hours ago, fiveworlds said:
For example, say I want many computers to download the same update file?
Free software such as BitTorrent is available to reduce server load.
QuoteThe BitTorrent protocol can be used to reduce the server and network impact of distributing large files. Rather than downloading a file from a single source server, the BitTorrent protocol allows users to join a "swarm" of hosts to upload to/download from each other simultaneously.
It's (I think) only useful if several users are downloading the same file(s) simultaneously.
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3 hours ago, John Bauer said:
The Bible is fairly explicit that it first happened in the sacred garden east of Eden, with Adam who lived somewhere around eight thousand years ago (more or less around the same time as Ötzi the "Ice Man").
Archbishop James Ussher used biblical research to calculate day 1 of creation as 23rd October 4004BC. Did he get it wrong?
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24 minutes ago, Conjurer said:14 hours ago, Carrock said:
The currently known violations are insufficient to produce the observed asymmetry but lack of evidence is not proof of nonexistence.
I believe that lack of evidence is definitely proof of nonexistence when it has been sufficiently sought after. If anti-matter bodies existed in the universe, then there would be huge anti-matter/matter explosions of energy, which simply don't exist.
You're just making things up.
CP violation is a subject of current research and certainly hasn't been 'sufficiently sought after.'
If you'd read the reference I gave - https://en.wikipedia.org/wiki/CP_violation#Matter–antimatter_imbalance you wouldn't find anything to even hint at the existence of 'anti-matter bodies.'
38 minutes ago, Conjurer said:Then real anti-matter which has been observed and researched on is not nearly as stable as normal matter. Then it decays quickly in the lab, and it is difficult to sustain.
No evidence exists of presumed stable particles such as antielectrons (aka positrons) or antiprotons decaying. Such particles can be contained indefinitely.
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10 hours ago, Conjurer said:
Furthermore, I believe the lack of abundance of anti-matter in the universe actually proves that the Big Bang did not originate from a particle pair fluctuation. It would have had to have been a single particle fluctuation.
Really? CP-symmetry violation produces matter/antimatter asymmetry.
The currently known violations are insufficient to produce the observed asymmetry but lack of evidence is not proof of nonexistence.
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5 minutes ago, dimreepr said:
What joke?
Good to know there wasn't one.
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17 minutes ago, dimreepr said:
That's a consequence of evolution rather than intelligence...
That's a consequence of evolution rather than intelligence...
Not that each has competence in different activities?!
Or am I insufficiently evolved to appreciate your joke!?
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Variations and consequences of the Laws of Thermodynamics
in Engineering
Posted
I'll respond to this and the previous post eventually (tomorrow at earliest). I have had limited time, combined with getting back into latex (inspired by comments from you a few months ago); there's some good looking perfectly safe free software but sorting out dependencies etc is a pain and I've been putting it off.