Entropy in everyday life

arfa brane said:
I've been thunking about this.

I don't think kilograms are logarithmic, or metres or seconds. What does that leave so there are "lots" of physical things, quantified logarithmically?
For say, a gas in a container, would it be acceptable to have a logarithmic volume? Why or why not?
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Depends on whether we're talking about logarithmic measurements, or logarithmic formulae.

  • The decibel unit is expressed as a logarithm of sound volume.
  • The Richter scale is a logarithm of earthquake intensity.
  • Saying CEOs make 7-figure salaries is measuring salaries logarithmically.
  • You could draw a chart of enclosure sizes, showing closets in the centimetre range, houses in the metre range and factories in the decametre range.
Those are all measurements. You graph them logarithmically. I'm trying to think of some natural processes that have a logarithmic formula.
 
Michael 345 said:
Consider this - there is a colony on the moon
They request a kg of XYZ
Do they mean a Earth kg XYZ, or a Moon kg of XYZ?

The concept has a different value depending on location
Now it would not matter if the moon orders a mass of XYZ
Earth would know the exact amount of mass of XYZ to send
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Actually, no.

The kg is a unit of mass. It is the same whether on the Earth or the Moon.

The Newton is the unit of weight. It equals 1 kg·m/s^2.
 
DaveC426913 said:
Depends on whether we're talking about logarithmic measurements, or logarithmic formulae.

  • The decibel unit is expressed as a logarithm of sound volume.
  • The Richter scale is a logarithm of earthquake intensity.
  • Saying CEOs make 7-figure salaries is measuring salaries logarithmically.
  • You could draw a chart of enclosure sizes, showing closets in the centimetre range, houses in the metre range and factories in the decametre range.
Those are all measurements. You graph them logarithmically. I'm trying to think of some natural processes that have a logarithmic formula.
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ΔG = -RT lnK?
 
exchemist said:
ΔG = -RT lnK?
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I was hopin' for something a little less cryptic. :)

I found some real-world examples of logarithmic correlations:

When you are trying to determine differences between two stimuli, your ability to discriminate follows a logarithmic law called the Weber’s law. The law states that the change in the stimulus that is needed for you detect a difference, is proportional to the magnitude of that stimulus.

1] Imagine lighting a candle in a dark room. It may seem very bright. But if you light the same candle under bright sun, you may have trouble seeing the flame.

2] If you are asked to judge which of two sounds are louder, you can detect a smaller difference when the sound are soft than when they are loud.

3] If you are asked to judge the difference in pitch between two sounds, you can detect a smaller difference when the pitch (frequency) is low than when the pitch is high.
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https://www.quora.com/What-things-i...arithmic-function-but-looks-like-linear-to-us

Here are some others. The curved lines show logarithmic relationships between the absolute intensity of the stimulus and the perceived magnitude.
main-qimg-743ae494ad27bd74f01b119e6d6021e1.webp
 
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DaveC426913 said:
I was hopin' for something a little less cryptic. :)

I found some real-world examples of logarithmic correlations:


https://www.quora.com/What-things-i...arithmic-function-but-looks-like-linear-to-us

Here are some others. The curved lines show logarithmic relationships between the absolute intensity of the stimulus and the perceived magnitude.
main-qimg-743ae494ad27bd74f01b119e6d6021e1.webp
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Oh well if you want one of those, you can have the pH acidity alkalinity scale.

The earlier one is the formula that relates the change in free energy of a chemical reaction to its equilibrium constant, i.e. the ratios of concentration (or pressure) of reactants and products at equilibrium for that reaction.
 
exchemist said:
Oh well if you want one of those, you can have the pH acidity alkalinity scale.
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As I thought through some examples I realized that there are two types of logarithmic representation. Most of them are nothing more than ways of visualizing data and using an easy to represent scale.
The Richter scale is one such example. The data is represented logarithmically -because the difference between 1 and 1.1 would be vanishingly small at the scale of 9 - it would essentially be 9 and 9.00000001. So we alter the scale in representations.

But that doesn't mean the physics of an earthquake itself is logarithmic in nature.

Electric shocks and sound volume are logarithmic though. There is a measurable correlation between input and output, and it is logarithmic.

I am not sure about pH scale though. Is the logarithm merely for easy visualization? Or is there a formula that shows the chemistry itself obeys a logarithmic scale?
 
Lots of physical systems exhibit exponential behavior.

An easy example is water in a tank or reservoir with a tap. Open the tap and the water pressure decreases exponentially over time (as the volume of water in the tank decreases).
Capacitors discharge through a fixed resistance exponentially.
I think it might be true in general, that energy tends to disperse exponentially.

It also might be true that any such process has a Taylor expansion. So what happens if you take logarithms of Taylor expansions? What can be visualised by doing that, and does it correspond to anything physical?
 
arfa brane said:
Lots of physical systems exhibit exponential behavior.

An easy example is water in a tank or reservoir with a tap. Open the tap and the water pressure decreases exponentially over time (as the volume of water in the tank decreases).
Capacitors discharge through a fixed resistance exponentially.
I think it might be true in general, that energy tends to disperse exponentially.
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Ah. Good point.
Heat loss is exponential too.
 
DaveC426913 said:
As I thought through some examples I realized that there are two types of logarithmic representation. Most of them are nothing more than ways of visualizing data and using an easy to represent scale.
The Richter scale is one such example. The data is represented logarithmically -because the difference between 1 and 1.1 would be vanishingly small at the scale of 9 - it would essentially be 9 and 9.00000001. So we alter the scale in representations.

But that doesn't mean the physics of an earthquake itself is logarithmic in nature.

Electric shocks and sound volume are logarithmic though. There is a measurable correlation between input and output, and it is logarithmic.

I am not sure about pH scale though. Is the logarithm merely for easy visualization? Or is there a formula that shows the chemistry itself obeys a logarithmic scale?
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The pH one is a log scale like the Richter scale. A tenfold increase in H+ concentration is one "click" up in acidity on the scale.

But the Gibbs free energy one is not. That free energy change is proportional to the log of the equilibrium concentration ratios.

There is a related one in electrochemistry (Nernst equation): https://en.wikipedia.org/wiki/Nernst_equation

Both derive from statistical thermodynamics, in which population distributions of species change in response to exponential energy change. Terms with exp(-E/kT) appear all over the place. So naturally it follows that equations for the energy are expressed in terms of the log of the numbers in the population distribution. :biggrin:
 
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exchemist said:
The pH one is a log scale like the Richter scale. A tenfold increase in H+ concentration is one "click" up in acidity on the scale.
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Yep. That much I know. What I am not sure of is whether there is indeed some physical manifestation of it that is logarithmic.
 
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And just like that, the discussion about entropy is done.

I'm reminded today of why I stopped posting here. The rudeness can be overwhelming at times. :(
 
wegs said:
And just like that, the discussion about entropy is done.

I'm reminded today of why I stopped posting here. The rudeness can be overwhelming at times. :(
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wegs, threads wander around.

If you have specific questions, with specific answers, the thread has a good chance of staying on topic. But you've got to admit, even your questions are sort of stream-of-consciousness, even if they have a common theme. We are following your lead.

Personally, I would be pleased as punch if I started a thread that generated enough interest to last 300 posts, regardless of how its content fluorished and multiplied.
 
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Entropy, hmm... o_O

I saw a person with a shirt that read: Youth is a gift of nature... Middle age is a work of art.

Next time I see him I'll tell him disorder increases with time, hence, he's lying to himself and that he is really going loony tunes stupid. :tongue:
 
Beer w/Straw said:
Entropy, hmm... o_O

I saw a person with a shirt that read: Youth is a gift of nature... Middle age is a work of art.

Next time I see him I'll tell him disorder increases with time, hence, he's lying to himself and that he is really going loony tunes stupid. :tongue:
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And just like that, Beer brought back entropy. lol

I saw a funny meme: ''Entropy: the ultimate Thermodynamics Game. You can't win. You can't break even. You can't even quit the game.'' :D
 
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