18
$\begingroup$

In laws of motion, everything has an equal and opposite reaction, and it applies to all matters in the reality.

If the earth stops moving suddenly just for one second, then everything on earth will be thrown out into space. But sudden rapid movement or sudden stop of motion does not cause the electrons to lose control around the nucleus or atom. Why? (For example: putting the brakes on suddenly in a car while traveling around the speed of $180$ km/h, creates massive momentum transfer and that momentum does not affect the electron's path of the car or the person sitting inside the car?) Is it because of the strength of the attraction between electron and nucleus?

NOTE: Thanks for the edit and I understand the transfer of momentum energy is transferred to the whole system, not just some part but still the momentum is high for an electron when 180 km/h suddenly stops, The whole atomic field will receive the massive vibrations caused by momentum and still the path of the electron is not disturbed in atomic level ? and is that because of the attraction between electrons and the nucleus?

Improve this question
$\endgroup$
6
  • 4
    $\begingroup$ A car acceleration can rarely exceeds 1g, at which point the question becomes "why don't electrons simply fall to the ground due to gravity?") $\endgroup$
    – Dmitry Grigoryev
    Commented Mar 7, 2022 at 15:10
  • $\begingroup$ I feel compelled to point out that while rotation keeps the earths surface moving at an impressive 1000 mph (roughly), escape velocity clocks in at 25,000 mph (roughly). So you're in for a traumatic impact as soon as your body touches anything considered part of the earth (rather than "on it"). But I don't see you making orbit. $\endgroup$
    – candied_orange
    Commented Mar 7, 2022 at 21:45
  • 1
    $\begingroup$ @candied_orange And if the Earth were to stop rotating, that would decrease the rotational speed of everything on it. Centripetal force comes from rotational speed relative to an inertial frame, not the co-moving frame of a rotating object. The Earth coming to a halt would change what the velocity relative to it of objects is, but would have no effect on their velocity relative to an inertial frame is (until friction makes them slow down). $\endgroup$
    – Acccumulation
    Commented Mar 7, 2022 at 22:45
  • $\begingroup$ @Acccumulation If you're considered "on it" and not magically halted then you wouldn't slow down until the traumatic impact with stuff that had magically halted. Now if we magically crank up the rotational speed to over 25 times you could fly off to space without needing any stopping. Why? Because the spinning creates a gravity like effect. Just in the other direction. $\endgroup$
    – candied_orange
    Commented Mar 7, 2022 at 22:56
  • 2
    $\begingroup$ I wonder: Is this question equivalent to: "What happens to the electrons when I hit a piece of steel hard with a hammer; will they change their 'orbit'?" $\endgroup$
    – U. Windl
    Commented Mar 8, 2022 at 11:55

6 Answers 6

Reset to default
21
$\begingroup$

At first, as others have said,- you transfer car momentum to a whole atom system, not just to some part of it,- like electrons, nucleus, etc.

Second,- an electron is not something you can easily mess around. If you look at the semi-classical Bohr atom model, an electron goes with a tangential speed around the nucleus defined by: $$ v={\sqrt {\frac {Zk_{\mathrm {e} }e^{2}}{m_{\mathrm {e} }r}}}. $$

So for example the electron in a hydrogen atom at the ground level flies with amazing $\approx 2000 ~\text{km/s}$ speed. That's about $1\%$ of light-speed! If converted to an electron centripetal acceleration notion, gives about $10^{21}\text {g}$. Thus an atom's electrodynamical system is a very stable thing.

That said, you can push an electron out of an atom. But for doing that you need some different approach, like scattering the hydrogen nucleus with high-speed neutrons in a particle accelerator or just "stretching" a hydrogen atom in a static electric field, so that it would overcome an ionization energy of $13~\text {eV}$, or forcing a hydrogen atom to absorb such an energy photon.

Improve this answer
$\endgroup$
6
  • $\begingroup$ But the electron is not actually moving at this speed or with this acceleration, right? Otherwise it would radiate away all its energy... $\endgroup$
    – Michael
    Commented Mar 6, 2022 at 22:47
  • $\begingroup$ @Michael, the electron is doing something around the nucleus of the atom that it is attached to, but as you say, it is NOT moving around the nucleus in a circular orbit or it would be radiating energy away. $\endgroup$
    – David White
    Commented Mar 7, 2022 at 3:37
  • $\begingroup$ @Michael Basically what you are defining here is an Ultraviolet catastrophe with which classical Physics was met long before. Solution is - quantum mechanics. It was noticed that electron emits energy in quanta $E=h\nu$. As electron is in the lowest energy state $n_1$ ground level,- it can't jump to even more lower state (no such state) and as such electron can't radiate even a bit. For example in Hydrogen what electron can radiate most is Lyman series by jumping $n_ {\ge 2} \to n_1$ $\endgroup$
    – Agnius Vasiliauskas
    Commented Mar 7, 2022 at 7:38
  • 3
    $\begingroup$ @Michael the calculation may be taking too long a detour through classical mechanics to be convincing, but an abbreviation to get the same result is to insert the Coulomb force law into Newton's law $F = ma$, yielding an acceleration of $\approx 10^{22} m/s^2 = 10^{21} g$ for an electron at at the radius of the hydrogen atom. I think a nice way of giving this an intuitive meaning is that the forces inside an atom are so much larger than those in the motions we experience everyday that we can think of chemistry (atomic forces) as something separate from mechanics (everyday forces). $\endgroup$
    – tobi_s
    Commented Mar 8, 2022 at 4:02
  • $\begingroup$ @AgniusVasiliauskas "In lower state electrons can't radiate a bit" if there is no energy in lower state then how would it move in such a speed (2000km/s)? Maybe it's due to attraction force around the nucleus but still it got kinetic energy at such speed, we cant say its cant radiate energy at lower state. $\endgroup$
    – Titan
    Commented Dec 14, 2022 at 7:38
20
$\begingroup$

The laws of motion you are quoting are the classical Newtonian mechanics laws. They do not hold as such at the quantum level, they are emergent for energies and distances where classical mechanics applies.

In your specific example the entity is the atom, a quantum mechanical bound state. The electrons are not separate from the nucleus as far as classical kinematics goes.The whole atom accelerates, not its individual components.

Improve this answer
$\endgroup$
13
  • 3
    $\begingroup$ "The whole atom accelerates, not its individual components." – But if I jab a helium atom with my finger, my finger doesn't apply a uniform force to the whole helium atom. I could well be mistaken, but I think what happens is that the outermost electrons of my finger repel the helium atom's electrons, but attract its protons. Overall, the repulsion is stronger, so even though the protons are attracted to my finger, the electrons will move away from my finger and carry the protons with them. $\endgroup$
    – Sophie Swett
    Commented Mar 6, 2022 at 19:17
  • 3
    $\begingroup$ @TannerSwett You are mistaken. The helium atom is a whole, unless a photon hits it with the energy level difference and kicks the electron out. One wavefunction describes the helium atom. If itinteracts , it interacts as a whole. $\endgroup$
    – anna v
    Commented Mar 6, 2022 at 19:22
  • 1
    $\begingroup$ @TannerSwett If the nucleus is hit with a neutron of sufficient energy the atom should change state. The atom is only 'a whole', meaning it does not change state, if there is not enough energy around. $\endgroup$
    – my2cts
    Commented Mar 6, 2022 at 22:16
  • 4
    $\begingroup$ But Anna it is well known that an atom will break if you hit it hard enough. In other words, if you make an atom accelerate hard enough, for example by rapidly bringing up another atom and having them collide, then the electrons will come off, just as the questioner is proposing. $\endgroup$
    – Andrew Steane
    Commented Mar 8, 2022 at 14:47
  • 1
    $\begingroup$ @BillyIstiak I'm a machine learning engineer but has a deep interest in space science along with particle physics, so, yeah I'm learning and I asked this question because I was sticking to the old theories of Bohr, thinking electrons as orbiting around the nucleus as the solar system, thats where I got so much of confusion. $\endgroup$
    – Titan
    Commented Mar 11, 2022 at 4:36
12
$\begingroup$

An acceleration of order $g\approx 10$ m/s$^2$ is utterly negligible compared to the acceleration of an electron in an atom.

Improve this answer
$\endgroup$
4
  • $\begingroup$ Best answer considering, but it woulld be cool to see a stack up or graph hinting at the flow of forces. After all, de-accelerating things can break them. $\endgroup$
    – Jason
    Commented Mar 7, 2022 at 22:34
  • 1
    $\begingroup$ Suppose an imaginary drone is traveling 60 km/sec inside the earth and suddenly if the earth stops for 1 sec then the drone wouldn't experience anything and deviate? simply because it's traveling more than the speed of earth how the momentum caused by earth can be avoided by drone when earth stops ? $\endgroup$
    – Titan
    Commented Mar 8, 2022 at 14:32
  • $\begingroup$ Assume the drone is the electron and earth as a macro matter which passes the vibrations of momentum to the drone. $\endgroup$
    – Titan
    Commented Mar 8, 2022 at 14:39
  • $\begingroup$ That's what we always tell to beginner. In Electrodynamics, we mostly ignore the effect of gravitational force since gravitational force is too negligible than other forces(magnetic force and electric force). $\endgroup$
    – Billy Istiak
    Commented Mar 10, 2022 at 17:51
2
$\begingroup$

There is a nice answer by @annav, I would like to give an example where a certain type of acceleration could in theory tear apart the atom. As you can see from the other answers, the atom is usually (in terms of acceleration) regarded as a quantum mechanical whole entity, and accelerates as a whole (like in your example).

Now here is the catch. The answer depends on the type (and form) of acceleration, that is, whether you are assuming in your example the same level of acceleration for the whole atom as an entity. That being said, the strong and EM forces holding the atom together are really "strong".

Anything above elementary particles should in theory be ripped apart, yes.

Spaghettification on an atomic scale?

But not infinitely strong. It is being theoretically suggested, that inside a black hole, the tidal forces could be stronger then the forces binding the atom, and in theory, the atom could be torn apart by the tidal effects of gravity. Why? Because the acceleration changes so rapidly, that different "parts" of the atom could undergo different levels of acceleration, and this, if the difference reaches a certain level, could overcome the binding forces, resulting in a torn atom.

Improve this answer
$\endgroup$
2
  • $\begingroup$ So the atomic bond is so strong and the energy transfer of momentum in day-to-day life doesn't matter to the atomic world? only the tidal force of black holes and particle accelerators can disturb the paths of electrons? right? if it's right then clearly the bonds between the elctron and nucleus is insane. $\endgroup$
    – Titan
    Commented Mar 8, 2022 at 14:43
  • 1
    $\begingroup$ @Titanium correct, and insane it is, the strong force that holds the quarks (into protons) is even stronger. $\endgroup$
    – Árpád Szendrei
    Commented Mar 8, 2022 at 18:20
2
$\begingroup$

But sudden rapid movement or sudden stop of motion does not cause the electrons to lose control around the nucleus or atom.

Sudden stop of motion is not something that occurs in nature but as a whole what you are describing is a collision event. Depending on the energies involved such collisions do have the potential to eject electrons from atoms. For example, at very high temperatures, thermal collisions may create a plasma of ions and free electrons.

In the case of the collision you are describing with speeds in the range of 180 km/h the energy is much to small to eject electrons and ionize matter. To achieve that you would have to up the speed to the range of tens of km/s. Think of a meteorite hitting the atmosphere or ground. In the case you are describing, the kinetic energy is converted into thermal energy and part of the thermal energy is converted into electromagnetic radiation (mainly in the infrared spectrum)

Like others have commented above, the view that electrons are small particles whizzing around the atomic nucleus on rigid orbits like planets around a star is totally outdated. Bohr and Rydberg presented it over hundred years ago. It was clear then that it can't be quite right since electrons should radiate energy when orbiting the nucleus. We know that all charged particles radiate energy when accelerated.

Our current understanding is that electrons bound to an atom exists in steady states each being described by a quantum mechanical wave function. Each electron state has a certain binding energy. However, these states can be influenced by external fields and thermal collisions creating non-uniform time-dependent charge distributions that radiate electromagnetic energy. As you are reading this your body radiates electromagnetic energy at an average rate of 100W.

Improve this answer
$\endgroup$
1
  • $\begingroup$ Nice explanation. Actually my thinking got wrong because of clinging to old Bohr and Rydberg theories. $\endgroup$
    – Titan
    Commented Mar 10, 2022 at 17:02
1
$\begingroup$

Some of the answers are implying that the answer lies within the quantum effects of the electron, but there's a pretty intuitive answer if you think of the system as classical -- and I suspect the quantum answer is just a slight modification of this.

If you could pull the nucleus of an atom on a string, there will be some speed where if you tug it too hard the electron will get left behind.

Comparing to your example: A car suddenly stopping will cause a person to fly into the windshield. But a car that doesn't stop as sudden will not cause a person to have any issues. This is because the friction between the person and the car keeps them in equilibirum dispite the additional inertial force.

Another example: If the was sun moved slowly enough, the planets would still follow it in orbit. But if the sun was jerked away too quickly, many or all of the planets could get left behind.

Improve this answer
$\endgroup$
3
  • $\begingroup$ I was not talking about the person flying to the windshield, I was asking what happens to the quantum dimensions of electrons. does the electron gets disturbed from its position ? but anyway, anna answered her best and it is far as good. $\endgroup$
    – Titan
    Commented Mar 8, 2022 at 18:31
  • 1
    $\begingroup$ Okay but you do understand what happens in the classical case right? You should think of what happens to the moon if the earth moves around slowly. If you think of an electron as orbiting the nucleus, you get the same intuition. $\endgroup$
    – Steven Sagona
    Commented Mar 8, 2022 at 18:33
  • $\begingroup$ The other necessary puzzle-piece for this classical intuition is just how fast the electrons are already moving, and thus what kind of order of magnitude of acceleration would be relevant to them in their "orbits". Agnius Vasiliauskas's answer includes those semi-classical numbers. $\endgroup$
    – Peter Cordes
    Commented Mar 13, 2022 at 13:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.