# Today's $1000 Question: How does the Atomic Force Work? This topic is 4480 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic. If you intended to correct an error in the post then please contact us. ## Recommended Posts I would like to know if someone can explain me how the atomic force works. I am especially interested in an equation. We have equations for gravity, the electrical force, etc... But I never actually saw an equation for the atomic force. I don't have$1000 to give you, however, so you're going to have to settle for my gratitude ;)

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Do you mean the strong nuclear and weak nuclear forces?

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If that's what you mean than this should explain it: Fundamental Forces

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The link didn't show up :(
Here: http://www.egglescliffe.org.uk/physics/particles/nuclearforces/nuclear.html

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By "atomic force" you mean strong force? (i.e. force that acts between quarks, and also keep nucleus)

I think there is no nice equations, because: it works only on short range, where you have to deal with quantum physics and where force carriers are (comparably) heavy.
Take for example electromagnetic forces. At big ranges with big charges you have nice equations. But force is not just some force attracting stuff together. It is transmitted by force carriers (electromagnetic forces is carried by photons). For electromagnetic force, nice equations is only approximation to what really happens. Same for strong force, except there is no nice equation.

Some info:
http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html

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Quote:
 Original post by DmytryTake for example electromagnetic forces. At big ranges with big charges you have nice equations. But force is not just some force attracting stuff together. It is transmitted by force carriers (electromagnetic forces is carried by photons). For electromagnetic force, nice equations is only approximation to what really happens. Same for strong force, except there is no nice equation.

that made me think: could the same be said about gravity? the graviton still isnt proven, is it? but if it were, how does that match up with einsteins interpretation about curving spacetime? extending the parralel, thatd mean the other forces could probably be tought of as curving spacetime aswell, no?

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Quote:
Original post by Eelco
Quote:
 Original post by DmytryTake for example electromagnetic forces. At big ranges with big charges you have nice equations. But force is not just some force attracting stuff together. It is transmitted by force carriers (electromagnetic forces is carried by photons). For electromagnetic force, nice equations is only approximation to what really happens. Same for strong force, except there is no nice equation.

that made me think: could the same be said about gravity? the graviton still isnt proven, is it? but if it were, how does that match up with einsteins interpretation about curving spacetime?

As I understand, quantum gravitation is one of the biggest problems of physics. Graviton should be a quanta of gravitational interaction, like photon is quanta of electromagnetical.
Quote:
 extending the parralel, thatd mean the other forces could probably be tought of as curving spacetime aswell, no?

Probably not - with gravity there's some really weird things happening (for example with orbit of Mercury), and them is explained by general relativity. On other hand, electromagnetic interaction does not exibit such strange effects.(i.e. there is different strangeness)

Besides, there is another very interesting thing: Other forces are interaction between some sort of charges, whereas gravity is interaction between energies*. There is only two known phenomena that works this way: inertia and gravity. And them are just too equal for concidence. It always makes sense to try to reduce two phenomena to one**, and that's what general relativity is all about.

*any form of energy - rest energy (as given by e=mc^2), or energy of photon, or whatever else. Note that energy depends to frame of reference, so it must have something to do with spacetime. It is probably possible to treat energy and impulse as sort of charge, though it will be very unlike any other charge.
**like electrical field and magnetic field.

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it just seems wrong two phemonena that appearently have completely different roots, like gravity and electromagnetism are so similar at the surface. it does feel like there should be a reason for that.

meh i know too little about all this.

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The reason I asked about the *strong* nuclear force is because I'm looking for a way to approximate it.

I am programming a simple simulator with the aim of simulating some basic elementary particles (electrons, neutrons, protons), and build virtual atoms using them. I won't try to be perfectly physically correct because I feel it would never end.

I will basically be simulating particles as points. So there will be no collision detection. And each timestep, all particles will apply their relevant forces to all other particles. In my case, I will worry about gravity, the electric force and the nuclear force, which will keep the nuclei from breaking apart... But I will also want to do something to keep electrons from crashing into the nuclei.

I'm mainly interested in a formula to compute the force (in terms of newtons) between particles. I'm also curious as about whether or not the nuclear force could be strong enough to keep electrons from crashing. Because then if they go too close to the nuclei, they will get bounced off.

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Quote:
 Original post by Eelcoit just seems wrong two phemonena that appearently have completely different roots, like gravity and electromagnetism are so similar at the surface. it does feel like there should be a reason for that.meh i know too little about all this.

Yes, it seems strange to me too. But on other hand, inverse squares law (at surface) is natural for fields that sorta conserve something. For example, "field" of bullets shot in random direction by the shotgun (in space), assuming bullets don't disappear and no new bullets is created in the space. Number of bullets per squared meter per second decreases as 1/r^2 .
Another example, apply simple "blur filter" to floating point image many times (to all image except some black and some white pixels used as sources as field). Gradient of resulting field will obey 1/r law in 2D and 1/r^2 in 3D. (with certain filters there could be anisotropy, but even in this case law will hold at least for parallel distance vectors) Seems that it doesn't matter what filter is used as long as filter doesn't change "brightness".

edit: another great example is things like deformations. Like heightfield of soap film - gradient obey 1/r law (on surface(pun intended)). I'm is not very sure about small 3D deformations in materials but it seems to me that there is some inverse squares law too.
Or sound, also inverse squares.

[Edited by - Dmytry on October 8, 2005 1:32:32 PM]

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is anyone aware of that huge machiene they made to measure gravity waves? it's like football field wide. crazy stuff

Tim

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Quote:
 Original post by timwis anyone aware of that huge machiene they made to measure gravity waves? it's like football field wide. crazy stuffTim

Aye, experiments for some things can get LARGE. For synchrotron radiation, circular paths with 1km diameter are used. I heard of a neutrino experiment that involved firing neutrinos from Chicago and then detecting them in the mines of Minnesota.

To the OP, computational simulations generally don't use some nice equation for potentials. Potentials are measured experimentally or calculated quantum mechanically for small systems (e.g. two particles). Then again, most simulations aren't at the sub-atomic level. Your best bet is probably to brush up on your QM. My guess is that no "clean" solution has been found for the forces you're looking at (i.e. we're no longer at the continuous limit).

Quantum mechanics was a great discovery, but got physicists less concerned with "truth" and more concerned with models that work within tolerance. The current atmosphere considers classical physics (Newton's mechanics, Maxwell's EM) to be just as true as modern physics (Einstein's relativity, Quantum mechanics). The difference is more in accuracy/precision than truth.

As for the similarity between gravitation and EM, it's probably a coincidence of sorts (like Dmytry said). Most of the mathematical results of classical physics could be reasoned out without any experiment (e.g. acceleration is slope of velocity curve is slope of position curve. I just "makes sense".). Of course, they were also concerned with "why". See light, why does it behave like it does? Because it always chooses the shortest distance to get where it's going, because every point radiates spherically, etc.

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Well I'd still like to have an idea of how much newtons of repulsive force a neutron can apply to a proton within a certain range, or an electron (although I guess physicists say there is no nuclear force applied to electrons, I'd still like to have an estimate...).

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Quote:
Original post by Dmytry
Quote:
 Original post by Eelcoit just seems wrong two phemonena that appearently have completely different roots, like gravity and electromagnetism are so similar at the surface. it does feel like there should be a reason for that.meh i know too little about all this.

Yes, it seems strange to me too. But on other hand, inverse squares law (at surface) is natural for fields that sorta conserve something. For example, "field" of bullets shot in random direction by the shotgun (in space), assuming bullets don't disappear and no new bullets is created in the space. Number of bullets per squared meter per second decreases as 1/r^2 .
Another example, apply simple "blur filter" to floating point image many times (to all image except some black and some white pixels used as sources as field). Gradient of resulting field will obey 1/r law in 2D and 1/r^2 in 3D. (with certain filters there could be anisotropy, but even in this case law will hold at least for parallel distance vectors) Seems that it doesn't matter what filter is used as long as filter doesn't change "brightness".

edit: another great example is things like deformations. Like heightfield of soap film - gradient obey 1/r law (on surface(pun intended)). I'm is not very sure about small 3D deformations in materials but it seems to me that there is some inverse squares law too.
Or sound, also inverse squares.

yeah well the inverse square law isnt that surprising an analogy, but what about the very concept of force? GR makes it pretty much redundant for gravity, it would seem odd that the concept would hold up for EM.

also, it would seem to me the weak and stong force arnt really forces in the classical sense of the word, they feel more like 'constraints' to me. somehow the notion of a nonconservative field doesnt fit in with the word force imo.

i remember reading about some model that explained the structure of atoms by viewing elementary particles as interlinked circles. it was kindof brief, but it did make a lot of sense inituatively, and was capable of correctly predicting all nuclei and their stability, or so it claimed.

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Quote:
 Original post by Max_PayneWell I'd still like to have an idea of how much newtons of repulsive force a neutron can apply to a proton within a certain range, or an electron (although I guess physicists say there is no nuclear force applied to electrons, I'd still like to have an estimate...).

neutrons and protons dont repell eachother afaik.
as for charged particles: EM should explain that all quite well, no?

in any case i dont think youre going to get very far with this, based solely on the fact that ive never run into any of these simulators, or videos or pictures of it. it would seem that whatever youre going to do, youre going to have to invent yourself.

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Proton = 3 quarks: 2 up, 1 down. 2/3e, 2/3e, - 1/3e providing a charge of 1e.
Neutron = 3 quarks: 2 down, 1 up. -1/3e, -1/3e, +2/3e providing a charge of 0e.

"it just seems wrong two phemonena that appearently have completely different roots, like gravity and electromagnetism are so similar at the surface. it does feel like there should be a reason for that.

meh i know too little about all this."

Perhaps it is because the universe is a closed system, a loop. Therefore, if space is curved, it may make sense that electromagnetic at the quantum level would be too.

Have you ever placed two mirrors side by side to get the infinite reflection effect?

Perhaps electromagnetics is 'echoed' in some manner, resulting in the strong nuclear forces/gravity/ etc.

Just a thought...

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Quote:
 Original post by Max_PayneI will basically be simulating particles as points. So there will be no collision detection. And each timestep, all particles will apply their relevant forces to all other particles. In my case, I will worry about gravity, the electric force and the nuclear force, which will keep the nuclei from breaking apart... But I will also want to do something to keep electrons from crashing into the nuclei.I'm mainly interested in a formula to compute the force (in terms of newtons) between particles. I'm also curious as about whether or not the nuclear force could be strong enough to keep electrons from crashing. Because then if they go too close to the nuclei, they will get bounced off.

What you really need is a basic lesson on quantum physics. It's not nuclear forces that keep the electrons from crashing into the nuclei. It's not even very meaningful to model an atom using Newtonian concepts like point particles orbiting each other, exerting forces on one another. In quantum physics particles are modeled as waves. What keeps an electron from crashing into the nucleus is that the electron can occupy only certain energy states, corresponding to certain standing wave patterns. To really be able to solve this kind of equations for anything more complicated than a hydrogen atom, you need a solid university level education. And then I'm not even talking about what goes on inside the nucleus...

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Does someone have approximate values of the radius of an electron and a neutron/proton, for the sake of scaling?

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electron is 1/2000 the mass of a proton but carries an equal and opposite charge.

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Quote:
 Original post by MooMansunelectron is 1/2000 the mass of a proton but carries an equal and opposite charge.

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Quote:
 Original post by Max_PayneI wasn't talking about the mass but the radius.

Scattering experiments doesn't show the electron to have any radius.

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Sorry, here:

The diameter of an electron is less than 1/1000 the diameter of a proton. A proton has a diameter of approximately 1/25,000,000,000,000 inch (0.000000000001 mm).

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Modern physics is really confusing. In modern models, electrons don't even have a radius, they are treated as a point mass. They don't have a position, they have a function that gives the probability of the electron having a position. Any pictures of nucleuses being clumps of neutrons and protons, or electrons orbiting nuclei, or whatever, these are just illustrations of simpler models of these things.

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It depends on what model you are using. The quauntum model is statistical. Other models do not need to be so vague.

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Quote:
 Original post by MooMansunSorry, here:The diameter of an electron is less than 1/1000 the diameter of a proton. A proton has a diameter of approximately 1/25,000,000,000,000 inch (0.000000000001 mm).

Where'd you get this info? In the standard physics model, fundamental particles (of which a proton isn't one, but an electon is), are point particles.