Molecule travelling speed wisdom

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Freedom physics
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#1
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A book says that water molecules in a breaker travel at hundreds or meters per second, I then looked up how fast molecules travel to double check and it said that air molecules travel at 500 metres per second! How are molecules able to travel this fast? Especially since when I pour water from a bottle it doesn't come traveling out at the speed of sound! 😄
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Freedom physics
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Oops the autocorrect wrote that title 😂
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Eimmanuel
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#3
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(Original post by Freedom physics)
A book says that water molecules in a breaker travel at hundreds or meters per second, I then looked up how fast molecules travel to double check and it said that air molecules travel at 500 metres per second! How are molecules able to travel this fast? Especially since when I pour water from a bottle it doesn't come traveling out at the speed of sound! 😄

It really depends on what you are actually referring to as the speed of water molecules in the liquid state.

If you are considering the Maxwell-Boltzmann velocity distribution of the water molecules in the liquid state, water molecules can have speed of the order of hundred metre per second based on the “thermal properties” of matter.
http://www.verticallearning.org/curr...01/page05.html

If you are thinking of the water molecules interacting with many other water molecules and can move around as shown in the “simulated motion in the liquid state” displayed in the following link:

https://chem.libretexts.org/Textbook...%2C_and_Solids

Then the speed of the water molecules is most likely to proportional to the self-diffusion coefficient of the water molecules. The speed in this case is slow which I don’t really have a reference.


This seems to be very similar what is known as drift velocity of electrons in metals. The drift velocity of electron is very small but the “thermal velocity” of electrons may over 1000 m/s.
https://www.quora.com/What-is-the-th...y-of-electrons
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morc13
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#4
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Think about it like they're vibrating. Things move fast when they vibrate just not large distances.
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DeBrevitateVitae
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#5
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(Original post by Freedom physics)
A book says that water molecules in a breaker travel at hundreds or meters per second, I then looked up how fast molecules travel to double check and it said that air molecules travel at 500 metres per second! How are molecules able to travel this fast? Especially since when I pour water from a bottle it doesn't come traveling out at the speed of sound! 😄
Eimmanuel answered your question very well so this might be redundant but I'll just add a quick lazy explanation:
The air molecules do travel at an average of 500m/s speed in betwen collisions with other molecules. But they are all travelling in different directions, changing direction after collision which gives an average velocity (adding up the vector components of each particle results, statistically, in them cancelling out) of anything from 0 to maybe a few m/s if you're blowing air through a vortex like that created by a small fan. It's like the difference between electron speed and drift velocity in wires. In between collisions, they travel very fast, but drift velocity is around 10^-3 m/s on a good day.
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Freedom physics
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#6
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(Original post by DeBrevitateVitae)
Eimmanuel answered your question very well so this might be redundant but I'll just add a quick lazy explanation:
The air molecules do travel at an average of 500m/s speed in between collisions with other molecules. But they are all travelling in different directions, changing direction after collision which gives an average velocity (adding up the vector components of each particle results, statistically, in them cancelling out) of anything from 0 to maybe a few m/s if you're blowing air through a vortex like that created by a small fan. It's like the difference between electron speed and drift velocity in wires. In between collisions, they travel very fast, but drift velocity is around 10^-3 m/s on a good day.
Thank you! Eimmanuel sorry, but I didn't know any of the things that you were referring to
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Eimmanuel
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#7
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(Original post by Freedom physics)
Eimmanuel sorry, but I didn't know any of the things that you were referring to
I also suspected you don't even know what are you asking or clearly knowing what you are asking.
Sometimes, students may think they are asking a simple question based on their current knowledge or understanding but it may turn out to have different interpretations.

If you are telling me, you don't know all the "stuffs" that I mention, I hope that you are studying A level physics on your own, or else your understanding of thermodynamics is pretty shallow or you are one of those who can remember and apply concepts without understanding them.

Maxwell-Boltzmann velocity or speed distribution is "a graph" that tell us that at a particular temperature, the molecules can have a distribution of speed when they are in thermal equilibrium. The distribution varies when the temperature changes.

https://www.khanacademy.org/science/...n-distribution

(Original post by Freedom physics)
...I then looked up how fast molecules travel to double check and it said that air molecules travel at 500 metres per second! ...
The speed that you quoted can be deduced from the Maxwell-Boltzmann velocity or speed distribution.

If you don't understand what I meant by "the speed of the water molecules is most likely to proportional to the self-diffusion coefficient of the water molecules.", I think it is ok because this is beyond A level.

If you tell me you don't know anything from the link given below (which I had posted above), you either did not even bother to look or you are just trolling in your reply (seem like what you like to do ) because the concepts are mainly from O level physics or chemistry known as kinetic particle theory or similar phrases.
https://chem.libretexts.org/Textbook...%2C_and_Solids

How the "speed of molecules" is connected to diffusion? Think about everyday phenomenon. If someone in your family is making some cookies with nice fragrance in the kitchen, you can smell them in your room. The molecules that make up of the fragrance have diffused randomly to your room at certain "drift speed" which depends on the "speed of the air molecules" at that temperature.
Similarly, in water, we observed such diffusion of potassium permanganate (VII) in water too.
https://www.youtube.com/watch?v=55CPfc9ij48
The rate of diffusion of potassium permanganate is depending on the "speed of the water molecules".

You can play with this simulation to see "relationship".
http://lab.concord.org/embeddable.ht...mperature.json
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Freedom physics
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#8
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(Original post by Eimmanuel)
The speed that you quoted can be deduced from the Maxwell-Boltzmann velocity or speed distribution.

If you don't understand what I meant by "the speed of the water molecules is most likely to proportional to the self-diffusion coefficient of the water molecules.", I think it is ok because this is beyond A level.

If you tell me you don't know anything from the link given below (which I had posted above), you either did not even bother to look or you are just trolling in your reply (seem like what you like to do ) because the concepts are mainly from O level physics or chemistry known as kinetic particle theory or similar phrases.
https://chem.libretexts.org/Textbook...%2C_and_Solids

How the "speed of molecules" is connected to diffusion? Think about everyday phenomenon. If someone in your family is making some cookies with nice fragrance in the kitchen, you can smell them in your room. The molecules that make up of the fragrance have diffused randomly to your room at certain "drift speed" which depends on the "speed of the air molecules" at that temperature.
Similarly, in water, we observed such diffusion of potassium permanganate (VII) in water too.
https://www.youtube.com/watch?v=55CPfc9ij48
The rate of diffusion of potassium permanganate is depending on the "speed of the water molecules".

You can play with this simulation to see "relationship".
http://lab.concord.org/embeddable.ht...mperature.json
Thanks so much! I understand everything now! I just want to make it clear that I never intend to be a troll and I'm now trying to make my questions as clear as possible, although for something like this i didn't think I had to state the conditions but I've learnt I have to 🙂
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Freedom physics
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#9
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#9
(Original post by DeBrevitateVitae)
Eimmanuel answered your question very well so this might be redundant but I'll just add a quick lazy explanation:
The air molecules do travel at an average of 500m/s speed in betwen collisions with other molecules. But they are all travelling in different directions, changing direction after collision which gives an average velocity (adding up the vector components of each particle results, statistically, in them cancelling out) of anything from 0 to maybe a few m/s if you're blowing air through a vortex like that created by a small fan. It's like the difference between electron speed and drift velocity in wires. In between collisions, they travel very fast, but drift velocity is around 10^-3 m/s on a good day.
Thank you, this did add appreciated thoughts to the conversation! 😄
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swinroy
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#10
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#10
(Original post by Freedom physics)
A book says that water molecules in a breaker travel at hundreds or meters per second, I then looked up how fast molecules travel to double check and it said that air molecules travel at 500 metres per second! How are molecules able to travel this fast? Especially since when I pour water from a bottle it doesn't come traveling out at the speed of sound! 😄
The most basic answer is that there are lots of molecules very close together travelling with a variety of High Speeds in RANDOM DIRECTIONS and they are too busy colliding with each other while you are pouring the water
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