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Useless ponderings about subatomic particles

  1. Jun 26, 2008 #1


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    Hi forum!

    I've always had a few useless ponderings:

    -Most articles I've read about classic vs. quantum physics say that, according to classic physics, electrons should spiral into and stick to their nucleus but I don't see why that would be. It seems to me that they would go through their nucleus, acquiring a very high momentum as they got close to it(since you can't say two points actually collided) and then lose the same amount of momentum gained as it went away from it. This would repeat. Take into account the higher mass of the nucleus (it would hardly move relative to the electron) and you have what looks like an electron orbiting its nucleus. This is, of course, according to classic physics.

    -How do neutrons manage to stay in the nucleus? I was wondering: if neutrons have no charge, how do we know they exist. I found that there are other forces that affect particles with no charge, such as gravity. So how do neutrons manage to stay in the nucleus if they don't behave exactly like protons? Also, I thought it would be nice for some reason if you multiply a subatomic particle's mass by its charge (either 1 or -1) to get a different kind of mass and think about them like that. But alas...

    Note that I'm just thinking about my textbook to hard.

    thanks for reading!
  2. jcsd
  3. Jun 27, 2008 #2


    You are talking about an electron that hasn't lost any energy but somehow its course changes causing it to shoot through the nucleus. You are correct that if this happened, damn that thing would be really flying when it buzzed by the protons!

    What the articles you've read are saying is that the electron should gradually lose energy due to electromagnetic radiation (charged particles radiate their kinetic energy as they move) and therefore sink down to a lower and lower orbit until they gradually collapse into a tiny spinning point (actually they would speed up as they sink but not enough to make up for the loss in potential energy by being closer to the protons). By the time they are grazing the protons, they've lost so much juice that they aren't moving fast enough to escape despite being right there at the center.

    If you need to convince yourself that moving charges radiate some of their energy away, just look at a radio. Antennas work this way. And when you drive under power lines, you hear a buzz because you are sucking up some of the energy radiated by the power lines (and you didn't even have to pay for it).

    You can read all about the discovery of neutrons on wikipedia. I think they were originally discovered by people studying radiation, because neutrons are one form of radiation. They can be observed because they can smack into other atomic nuclei and knock out protons, which obviously are a lot noisier when evicted. Yes, classically it's hard to imagine a collision between particles. But we do not live in a classical world.

    Nuclear fission (the thing that powers nuclear reactors) is all about neutrons. Without neutrons, nuclear reactors wouldn't exist and Hiroshima and Nagasaki would not have memorials. A splitting atom throws out some very high-energy neutrons which then go out and explode other nearby atoms like a bullet through an apple. All those atoms and pieces of atoms flying around create tremendous heat which boils water which creates steam which turns turbines which turn magnets which induce current in wires which powers your hair dryer. But this chain recation only keeps going if you have a kind of atom whose nucleus is spring-loaded and ready to blow, or "fissionable" as technical people say.

    Also, it can be easily seen (by glancing at a periodic table) that the number of protons in a nucleus does not account for all of its mass. The atomic mass of hydrogen is about 1 AMU, but the mass of helium is about 4 AMU. However, Hydrogen has one proton and Helium has two. Clearly there is another source of mass there!

    I've got a better question for you: how do the protons stay in the nucleus at all? They are like charges, so they repel, right? Shouldn't they fly apart like they hate each other? The reason they don't is that there is another force which sticks protons and neutrons together. It is called the strong force. This force only has a significant effect at very close range, and only works between particles that are made of quarks. Protons and neutrons are both made of quarks. This force is insanely strong (hence the name) and complicated enough that people apparently can't understand it without quantum physics. So I'll stop there.

    You can define any quantity you want, but I can't think of any case where that number (let's call it "chmass") could be useful.
  4. Jun 27, 2008 #3


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    1) Circular motion is acceleration, electric charges under acceleration will emit radiation, i.e loose energy. What will happen to the electron around the nucleus if is looses energy for each revelation? Answer: radius will decrease - i.e spiral motion.

    2) As Xezlec told you, in the nucleus we have two forces. Replusive electromagnetic, and attractive 'srong nuclear force'. You might want to google things also, like 'nuclear force', 'nuclear physics' and also 'detection of neutrons'

  5. Jun 27, 2008 #4


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    Last edited by a moderator: May 3, 2017
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