Equating motion with energy

[swansont]

 

Dear Studiot,

 

Please note that I have no argument against ‘Kinetic theory of gas’. My doubt (expressed in my first post) is how come an assumption used in it has transformed itself into a real fact without a proper mechanism that relates them and lead towards equating energy with motion (by many). I think it is only fair that a logical mechanism of action is required before equating them. In other words, I am interested to know how does energy move a matter-particle.

 

Thanks,

Nainan

 

 

That's fairly simple: it doesn't. Energy isn't a substance, it's a property. Energy doesn't make something move, it's a property that moving objects have. It's a useful property to keep track of because the total amount is conserved.

[studiot]

 

My doubt (expressed in my first post) is how come an assumption used in it has transformed itself into a real fact without a proper mechanism that relates them and lead towards equating energy with motion (by many).

 

That is not the same as how does energy move a matter particle?

 

Surely since the word kinetic means 'to do with motion' it is not suprising that any kinetic theory of anything at all is about motion?

 

But motion of what?

 

Well motion of particles.

 

The original 'particles' were proposed before molecules were 'discovered'.

So they were only equated with molecules later in the development of physics and still to this day do not need the existence of molecules for particulate theory to hold good.

 

So what is a particle?

 

Here is DF Lawden (Professor of Mathematics University of Canterbury NZ) on Particles

 

 

A particle is defined to be a body whose dimensions are negligable to the degree of accuracy in linear measurement to which we chose to work. The Earth is a body of 4000 miles radius whereas the the radius of its orbit about the Sun is over 93,000,000 miles. If therefore it is sufficient to specify the orbit to an accuracy of 0.1% then the Earth may be treated as a particle.

 

Using these definitions we can develop the whole conventional theory of rigid and fluid body motion and interaction without further ado.

 

We start by observing that solids are a continuum and that when solids melt there is almost no expansion so we postualte that liquids are also a continuum.

We then divide up the liquid into lots of adjacent fluid mechanical particles to develop fluid mechanics,

We note that a when a given fluid turns into a gas it expands considerably - Water expands approximately 1700 times.

 

So do we postulate that the particles expand 1700 times when water evaporates and shrink again when the steam condenses?

 

Or do we postulate that the particles separate and there is space between them?

 

Can you think of a simple experiment to test which is correct?

 

This is the basis of the original kinetic theory.

The application of Lawden's mathematics came later.

 

Of course as soon as we do some mathematics we can attribute an energy due to motion or kinetic energy to each particle and we are in business of developing a mathematical kinetic theory. (It was not Lawden who did this).

 

Again it is simple to observe by stirring a liquid that some particles move fast and some move more slowly and that energy is transferred from the fast ones to the slow ones as might be expected from the observation that when to particles collide or just brush past the faster particle can hit harder (carries more energy) than the slower one.

 

So now can you answer my question.

 

Have you ever seen Brownian motion, since your last comments suggest you are unsure as to what exactly it is?

 

Oh and please note that all this would work just as well if there were no 'molecules'.

Edited August 18, 2014 by studiot

[matterdoc]

Dear Studiot,

You can see my views on Brownian movements at http://vixra.org/abs/1103.0117

Nainan

[studiot]

I didn't ask for your views on it just if you have ever seen it for yourself?

 

Surely this is a simple question that does not warrant a link to 5 page pdf?

 

Am I wasting my time trying to engage you in friendly discussion or did my last post#27 merit no other comment?

Edited August 19, 2014 by studiot

[Strange]

Dear Studiot,

You can see my views on Brownian movements at http://vixra.org/abs/1103.0117

Nainan

 

"There is neither a logical cause nor a mechanism nor a known mover, acting on liquid molecules. Hence, root cause of Brownian motion remains a mystery."

 

In what way is the motion of molecules not a an explanation?

 

I see that your 5 page vixra (aka crank) article does not present an alternative model and is therefore of no value.

[Sensei]

Please note that I have no argument against ‘Kinetic theory of gas’. My doubt (expressed in my first post) is how come an assumption used in it has transformed itself into a real fact without a proper mechanism that relates them and lead towards equating energy with motion (by many).

 

Isn't it basic observation that you can perform in f.e. kitchen, not to mention lab.. ?

Burned fuel (typically methane) is releasing energy via reaction:

CH₄ + 2 O₂ -> CO₂ + 2 H₂O

 

Input molecules have little kinetic energy (especially if we're burning liquid or solid fuel), and products are highly accelerated gas molecules.

 

You can reverse this process, by cooling down gas molecules, and they will be back liquid. Which is used quite often in distillation.

 

 

I think it is only fair that a logical mechanism of action is required before equating them. In other words, I am interested to know how does energy move a matter-particle.

 

Photon has energy E=h*f.

When it's absorbed by charged particle such as proton or electron, it's disappearing from the system, but energy must be conserved, therefor particle that absorbed it is accelerated.

It can scatter to other particles and give them all or part of kinetic energy, and larger and larger amount of particles is accelerated. Suddenly absorbed energy is spread across billions of particles/molecules.

 

[swansont]

 

 

Photon has energy E=h*f.

When it's absorbed by charged particle such as proton or electron, it's disappearing from the system, but energy must be conserved, therefor particle that absorbed it is accelerated.

It can scatter to other particles and give them all or part of kinetic energy, and larger and larger amount of particles is accelerated. Suddenly absorbed energy is spread across billions of particles/molecules.

 

 

It's also a matter of a photon having momentum, which is classically the connection with there being a force (or impulse). A photon being absorbed relies on there being an internal structure to system to allow for an excitation. A photon incident on e.g. a bare electron cannot be absorbed, because momentum and energy can't be simultaneously conserved. The photon is scattered.

 

Thus the premise that is involved in "how does energy move a matter-particle" seems to me to be simplistic to the point that it's flawed. Energy and motion are not so directly connected.

[Sensei]

It's also a matter of a photon having momentum, which is classically the connection with there being a force (or impulse). [...]

 

A photon incident on e.g. a bare electron cannot be absorbed, because momentum and energy can't be simultaneously conserved. The photon is scattered.

You're probably thinking about angular momentum, not linear momentum.

 

Because in Compton scattering most certainly linear momentum is not conserved.

 

It's even more or less visiblely said in article

http://en.wikipedia.org/wiki/Compton_scattering

 

Quote from article:

"Note that the momentum gained by the electron (formerly zero) exceeds the momentum lost by the photon:"

 

After making calculations for f.e. angle = 180 degrees ([latex]\frac{h}{m_e*c}*2[/latex]) we can see that incoming photon with E=511 keV (wavelength=2.42 pm) is giving 340 keV to electron (it's now on its kinetic energy), and new photon with 170.5 keV (wavelength=7.27 pm) is created (Inquisitive person would ask how long it takes such scattering, how long photon is fully absorbed prior emitting new one).

 

 

Electron with K.E.=340510 eV has gamma=1.666 and v=0.8c

 

Momentum of incoming photon: 2.73804545454545E-022

Momentum of incoming electron: 0

Momentum of outgoing photon: 9.11139146152144E-023

Momentum of outgoing electron: 3.64081441381092E-022

 

A photon being absorbed relies on there being an internal structure to system to allow for an excitation.

Example Compton scattering on electrons shows that particle doesn't need to have internal structure to being accelerated.

 

In early quantum physics proton was also thought to have no internal structure.

It also might change with electron, when somebody will find out incontrovertible experimental proof.

But there is needed open mind to be able to realize it in the first place.

 

ps. I am attaching OpenOffice SpreadSheet, so anyone can quickly reproduce calcs.

Compton Scattering Angle 180 Calcs.zip

Edited August 27, 2014 by Sensei

[swansont]

 

You're probably thinking about angular momentum, not linear momentum.

 

Because in Compton scattering most certainly linear momentum is not conserved.

 

 

I think perhaps you misread my post. In Compton scattering the photon is scattered, not absorbed. You can't simultaneously conserved energy and momentum were an electron to absorb a photon. Thus, the electron must scatter the photon. As I said above.

[imatfaal]

 

You're probably thinking about angular momentum, not linear momentum.

 

Because in Compton scattering most certainly linear momentum is not conserved.

 

It's even more or less visiblely said in article

http://en.wikipedia.org/wiki/Compton_scattering

 

Quote from article:

"Note that the momentum gained by the electron (formerly zero) exceeds the momentum lost by the photon:"

...\snip snip

 

OK - I am confused. Cos it also says this

 

Because the mass-energy and momentum of a system must both be conserved, it is not generally possible for the electron simply to move in the direction of the incident photon. The interaction between electrons and high energy photons (comparable to the rest energy of the electron, 511 keV) results in the electron being given part of the energy (making it recoil), and a photon containing the remaining energy being emitted in a different direction from the original, so that the overall momentum of the system is conserved. If the scattered photon still has enough energy left, the process may be repeated.

 

 

 

My reading is that it is because momentum (and energy) is conserved for the system that idea arises and scattering takes place.

[swansont]

My reading is that it is because momentum (and energy) is conserved for the system that idea arises and scattering takes place.

That's exactly it. You have to go to a two-dimensional result with a scattered photon to find a solution that's valid. It's a standard "modern physics" HW or test question to show that absorption (or colinear scattering) violates one of the conservation laws or otherwise has no solution.

 

 

Because in Compton scattering most certainly linear momentum is not conserved.

 

It's even more or less visiblely said in article

http://en.wikipedia.org/wiki/Compton_scattering

 

Quote from article:

"Note that the momentum gained by the electron (formerly zero) exceeds the momentum lost by the photon:"

Sorry, I missed this before. It's a poorly-worded statement; I think whoever wrote it was referring to a classical calculation, which does not apply. (They mention relativistic mass, so there's a cap on how good it's going to be)

 

Immediately following that statement is a derivation using relativistic conservation of momentum which yields the Compton scattering formula.

 

edit: I think the wiki article is assuming colinear motion, as it's a scalar equation, so it's not surprising that they find a contradiction. Momentum is a vector, and you have to treat it as such. Solving it as a scalar is the same as assuming 1D.

[Sensei]

 

edit: I think the wiki article is assuming colinear motion, as it's a scalar equation, so it's not surprising that they find a contradiction. Momentum is a vector, and you have to treat it as such. Solving it as a scalar is the same as assuming 1D.

 

Yes, I know momentum is vector (similar like velocity is vector).

 

Sorry, but please show me using vector math how incoming photon with E = 510999, with wavelength=2.42 pm, and momentum p= h / 2.42*10^-12 = 2.738e-022 (let's simplify it that it's going in +x axis)

will lead to electron with higher momentum p = m_e * 0.8 * 299792458 * 1.6666 = 3.6408e-022 (Relativistic kinetic energy = 340 keV)

and scattered photon with E = 170500 eV, wavelength = 7.27 pm, and momentum p = h / 7.27*10^-12 = 9.11139e-023.

(these data are result of Compton scattering formula for angle = 180 degrees)

[swansont]

 

Yes, I know momentum is vector (similar like velocity is vector).

 

Sorry, but please show me using vector math how incoming photon with E = 510999, with wavelength=2.42 pm, and momentum p= h / 2.42*10^-12 = 2.738e-022 (let's simplify it that it's going in +x axis)

will lead to electron with higher momentum p = m_e * 0.8 * 299792458 * 1.6666 = 3.6408e-022 (Relativistic kinetic energy = 340 keV)

and scattered photon with E = 170500 eV, wavelength = 7.27 pm, and momentum p = h / 7.27*10^-12 = 9.11139e-023.

(these data are result of Compton scattering formula for angle = 180 degrees)

 

I don't see what the problem is. Recoil photon is in the opposite direction. That always leads to a higher magnitude of momentum of the target than what you started with. The scattered particle's momentum picks up a - sign from going in the other direction.

 

 

Not grabbing a calculator and dropping the exponent, the initial momentum is ~2.74 and the final momentum is 3.64 - .91 = 2.73

 

Is the issue with the last digit discrepancy? I assume that's just roundoff.