Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: granpa on 28/06/2016 18:17:18
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a chemical reaction might release 10 ev of energy.
a nuclear reaction releases millions of times that.
we are told that that is because the nuclear force is much stronger.
At first that seems to make perfect sense but upon closer inspection the numbers clearly dont work out.
The strong force is only 100 times as strong as electromagnetism and it only acts over a very short distance (about the size of the nucleus or 1/10,000 of an angstrom)
now energy = force * distance
so 100 * (1/10,000) = 0.01
even though the force is stronger it should release much less energy.
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Obviously something is amiss: either the analysis or the experimental results... I believe that the experimental data is correct, therefore the analysis presented here must be flawed.
force * (distance that an object moves under the action of said force) = (energy expended to exert said force on said object)
One must be very careful when plugging terms into equations, lest they use the wrong meaning of... distance, for instance.
I am also not quite sure what is meant by "the strong force is 100 times as strong as electromagnetism..."
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Surely the energy released in a nuclear explosion is the result of the annihiliation of some matter and not related to the strong force itself?
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a chemical reaction might release 10 ev of energy.
a nuclear reaction releases millions of times that.
we are told that that is because the nuclear force is much stronger.
We are not told that. May I inquire where you got that idea from?
The energy released in nuclear reactions is actually electrostatic potential energy. To construct a nucleus out of protons and neutrons requires assembling them together. In order to do this one has to do work to overcome the electrostatic repulsion between the protons. The force that holds the nucleus together after bringing the protons together is the strong force. This is a fact which is unfortunately never pointed out.
Your confusion arises because you're confusing energy with force. Its electrostatic energy that's stored in the nucleus. It's the strong force that holds the nucleus together.
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a chemical reaction might release 10 ev of energy.
a nuclear reaction releases millions of times that.
we are told that that is because the nuclear force is much stronger.
We are not told that. May I inquire where you got that idea from?
The energy released in nuclear reactions is actually electrostatic potential energy. To construct a nucleus out of protons and neutrons requires assembling them together. In order to do this one has to do work to overcome the electrostatic repulsion between the protons. The force that holds the nucleus together after bringing the protons together is the strong force. This is a fact which is unfortunately never pointed out.
Your confusion arises because you're confusing energy with force. Its electrostatic energy that's stored in the nucleus. It's the strong force that holds the nucleus together.
That would explain fission but it would not explain Fusion which is even more energetic than fission
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That would explain fission but it would not explain Fusion which is even more energetic than fission
Actually it does explain fusion. But you have to realize that it's fusing two deuterium nuclei together which releases more energy than splitting a U(235) atom. Speaking in general terms like "fusion is more energetic than fission" is incorrect and will lead to errors.
But I'm curious. What makes you think that it doesn't explain fusion? I assure you that it does. If pressed I'll work it out for you. However when I do something like this I make it into a project. That means that I make it into a webpage under my website. That way when this subject comes up again I won't have to repeat myself. However it may take a very long time since I have other things that I do with my time. It won't be a priority. But I may be able to whip something together for a quick reply. After all it appears that the problem here is a lack of understanding of the nature of energy from nuclear reactions as well as antimatter/matter reactions (for completeness).
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Surely the energy released in a nuclear explosion is the result of the annihiliation of some matter and not related to the strong force itself?
No. Matter is not annihilated in nuclear explosions. All that happens is that atoms are either fused together or split apart. The number of protons and neutrons remain the same.
However when matter annihilates antimatter it can result in producing only photons. That happens when an electron annihilates a positron, two photons are produced. However when a proton smashes into an antiproton the result isn't always just photons.
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Is that the case for nuclear fusion? Surely some of the mass (I should have said that instead of matter) is converted into energy?
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That would explain fission but it would not explain Fusion which is even more energetic than fission
Actually it does explain fusion. But you have to realize that it's fusing two deuterium nuclei together which releases more energy than splitting a U(235) atom. Speaking in general terms like "fusion is more energetic than fission" is incorrect and will lead to errors.
But I'm curious. What makes you think that it doesn't explain fusion? I assure you that it does. If pressed I'll work it out for you. However when I do something like this I make it into a project. That means that I make it into a webpage under my website. That way when this subject comes up again I won't have to repeat myself. However it may take a very long time since I have other things that I do with my time. It won't be a priority. But I may be able to whip something together for a quick reply. After all it appears that the problem here is a lack of understanding of the nature of energy from nuclear reactions as well as antimatter/matter reactions (for completeness).
I'll thank you in advance for your project.
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We are not told that. May I inquire where you got that idea from?
The energy released in nuclear reactions is actually electrostatic potential energy. To construct a nucleus out of protons and neutrons requires assembling them together. In order to do this one has to do work to overcome the electrostatic repulsion between the protons. The force that holds the nucleus together after bringing the protons together is the strong force. This is a fact which is unfortunately never pointed out.
Your confusion arises because you're confusing energy with force. Its electrostatic energy that's stored in the nucleus. It's the strong force that holds the nucleus together.
The bolded part is very wrong.
http://theory.uwinnipeg.ca/mod_tech/node178.html
The Strong Nuclear Force and Binding Energy
It may seem strange that nuclei, being composed of positively charged protons and neutral neutrons packed very closely together, are able to exist. One might think that the large repulsive electrostatic forces between the protons should cause the nuclei of atoms to fly apart. Obviously, most nuclei are stable and thus there must exist some other force which binds them together. This force is known as the nuclear force and is an attractive force that acts between all nuclear particles at the short distances between them (about 2 x 10-15 m). Within the nucleus, where the protons and neutrons are very close together, the nuclear force dominates the repulsive Coulomb force and holds the nucleus together.
One important illustration of the equivalence of mass and energy of Equation (13.2) has to do with what is called the binding energy of the nucleus. It is observed that the mass of any nucleus is always less than the sum of the masses of the individual constituent nucleons which make it up. The ``loss'' of mass which results when nucleons form a nucleus is attributed to a ``binding energy'', and is a measure of the strength of the strong nuclear force holding the nucleons together. In order to separate the nucleons, energy must be supplied to the nucleus. This is usually accomplished by bombarding the nucleus with high energy particles (atom smashing).
The reason the binding energies of the strong force between nucleons is so much greater the the electromagnetic binding energies between electrons and nuclei is down to both strength and distance. In the nucleus protons and neutrons are on average about 10,000 times closer than the average position of an electron to a nucleus. The strong force is also approximately 100 times stronger than electromagnetism. At the distances in the nucleus the strong force has a roughly 1/r^2 dependence. Therefore at nuclear distances we expect the attraction of the strong force to be about 10,000*100 or 1,000,000 times stronger based on both the increased strength and decreased distance. These numbers are very approximate but good to an order of magnitude.
The electrostatic interaction is repulsive and actually reduces the binding energy (i.e. pushes things apart). But since the distances in the nucleus are closer to 50,000 times smaller than the electron-nucleus distance and the strong force is closer to 137 times stronger than the electromagnetic force including the decrease in binding energy from electrostatic repulsion still results in nuclear binding energies that are on the order of a million times higher than the electron binding energies.
During nuclear reactions that energy that is released comes from the mass defect. The mass defect occurs because the binding energy of the nucleons is more negative before than reaction that after the reaction. The strong force is the attractive force that binds the nucleons together and therefore is the source of the mass defect and the energy released during the reaction. The electrostatic interactions are repulsive and actually work to slightly decrease the mass defect by making the binding energy less negative.
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Angular momentum of electron = (planks constant)/(2pi)
Relativistic angular momentum = γmvr
Relativistic centripetal force = γmv^2/r
Gamma*(electron mass)*c*(10^-14 m)=(planks constant)/(2pi) solve for x
Wolfram says gamma = 38.6
38.6*(electron mass)*(velocity of light)^2/(10^-14 m)
Wolfram says force = 316 newtons
The force between 2 electrons at that distane is
( Coulomb's constant )*(electron charge)^2/(10^-14 m)^2
Wolfram says 2.3 newtons
According to those equations the force is 137 times stronger than electromagnetism would be at that distance and that is sufficient for the electron to fit inside a neutron
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Angular momentum of electron = (planks constant)/(2pi)
Relativistic angular momentum = γmvr
Relativistic centripetal force = γmv^2/r
Gamma*(electron mass)*c*(10^-14 m)=(planks constant)/(2pi) solve for x
Wolfram says gamma = 38.6
38.6*(electron mass)*(velocity of light)^2/(10^-14 m)
Wolfram says force = 316 newtons
The force between 2 electrons at that distane is
( Coulomb's constant )*(electron charge)^2/(10^-14 m)^2
Wolfram says 2.3 newtons
According to those equations the force is 137 times stronger than electromagnetism would be at that distance and that is sufficient for the electron to fit inside a neutron
What you've calculated is at best the amount of centripetal force needed to keep the electron in the neutron. The electrostatic force would have to be equal to or greater than that value for the electron to be inside the neutron. You've actually proven that an electron can't be confined to a neutron. The electrostatic force would have to be at least 137 times as big as it is to allow the electron to be inside the neutron.
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Angular momentum of electron = (planks constant)/(2pi)
Relativistic angular momentum = γmvr
Relativistic centripetal force = γmv^2/r
Gamma*(electron mass)*c*(10^-14 m)=(planks constant)/(2pi) solve for x
Wolfram says gamma = 38.6
38.6*(electron mass)*(velocity of light)^2/(10^-14 m)
Wolfram says force = 316 newtons
The force between 2 electrons at that distane is
( Coulomb's constant )*(electron charge)^2/(10^-14 m)^2
Wolfram says 2.3 newtons
According to those equations the force is 137 times stronger than electromagnetism would be at that distance and that is sufficient for the electron to fit inside a neutron
What you've calculated is at best the amount of centripetal force needed to keep the electron in the neutron. The electrostatic force would have to be equal to or greater than that value for the electron to be inside the neutron. You've actually proven that an electron can't be confined to a neutron. The electrostatic force would have to be at least 137 times as big as it is to allow the electron to be inside the neutron.
But the strong force is strong enough
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But the strong force is strong enough
Too bad electrons aren't made of quarks and don't have color and thus aren't subject to the strong force.
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Is that the case for nuclear fusion? Surely some of the mass (I should have said that instead of matter) is converted into energy?
On second thought I may be wrong about the energy in the nucleus being all electrostatic in nature. Let me get back to you on that.
By the way, mass cannot be converted into energy. That's a common misconception. See:
Does nature convert mass into energy by Ralph Baierlein, Am. J. Phys. 75 4, April 2007;
http://www.newenglandphysics.org/other/mass_into_energy.pdf
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Well, I pride myself by being able to admit when I'm wrong and this is one of those times. I was wrong when I said that nuclear energy is electrostatic energy. That assertion was wrong. It's only a minor portion of the nuclear energy. Here are two responses that I got when I asked if the energy in the nucleus is electrostatic
False. This is true of ATOMS (though of course you meant the total
energy---kinetic as well as potential), but not of nuclei, where the
strong force is dominant (electromagnetic forces make a small contribution).
..., the electrostatic contribution is small. The main energy is due to
the strong force, not the electromagnetic.
The easiest way to understand the energy budget of a nucleus is to look at the semi-empirical liquid-drop mass formula. Besides the rest masses of protons and neutrons, the main terms are the surface-tension term (from nuclear forces that bind the nucleons) and the electrostatic energy associated with proton-proton repulsion. In fission of heavy nuclei, electrostatic energy is released, but some extra surface energy gets stored (because the net surface area increases). In fusion of light nuclei, extra electrostatic energy is stored, but some surface energy is released (because the net surface area decreases). The energy released in these reactions can be calculated quite accurately from the liquid-drop mass formula.
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See here for details of the Liquid Drop Model of the nucleus.
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/liqdrop.html (http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/liqdrop.html)
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A minor point what is an angstrom, could we please have SI units
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1 angstrom (1 Å) is 10–10 meters.
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1 angstrom (1 Å) is 10–10 meters.
How much in layman terms please?
The Strong Nuclear Force (also referred to as the strong force) is one of the four basic forces in nature (the others being gravity, the electromagnetic force, and the weak nuclear force).
As its name implies, it is the strongest of the four. "However, it also has the shortest range", meaning that particles must be extremely close before its effects are felt.
Thus I doubt if any useful energy could be got out of the strong force?
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It powers the sun
1 Angstrom is about the size of an atom
The nucleus is 10,000 to 100,000 times smaller