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phlogiston
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Quote: Originally posted by woelen  | | The energy, mentioned bij aga, is coming from the person who put the nail somewhere far away from the magnet. |
I believe this to be true, but in my mind it raises the following puzzling question:
When you magnetize a piece of iron, potential energy between it and every nail in the universe is increased. How does the universe know how much
energy it should take to magnetize a piece of iron?
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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woelen
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The universe does not need to know. The fact that you magnetize your nail only is "communicated" to the surrounding space with at most the speed of
light. So, a nail in the Andromeda galaxy does not feel your magnetized in the next 2.5 million years or so.
Another thing is that the strength of the associated fields fall off quadratically with distance. How much iron do you think will be needed in the
Andromeda galaxy to be felt by your nail?
Yet another thing is that what we conceive of as a continuous field, in reality is a discrete exchange of so-called messanger particles. Your nail and
the iron in the Andromeda galaxy exchange messanger particles (for electromagnetic forces the messanger particles are photons). But probably a single
messanger particle already is way too much for taking into account the minute forces between your nail and the iron in the Andromeda galaxy. The only
effect of far away iron may be some extremely low frequency quantum noise in the perceived magnetic force, acting on your nail.
So, in reality, the effect of a magnetized nail is limited to a certain surrounding environment.
Gravitational forces and electromagnetic forces fall off quadratically with distance and that makes them long range forces. With gravity the long
range effect is larger, despite being very weak in an absolute sense, because of the fact that there is only one sign for masses. We have no negative
gravity, which can compensate for attracting forces.
Nuclear forces fall off much more rapidly. Weak nuclear forces fall off exponentially, the potential can be written as -K*exp(-mr)/r with r being the
distance between the interacting objects, K and m being certain positive constants. The factor exp(-mr) only needs to be taken into account at a scale
of nuclear radii (which is in the order of magnitude of 10000 times as small as atomic radii), so at an atomic scale this force is at the order of
magnitude of 10^(-1000) or so smaller than at nuclear scale. For strong nuclear forces I do not know the rate at which they fall off. These forces do
not really fall off, they are so strong that particles always are close to each other. It simply is not possible to have particles further away for
strong nuclear forces (which act at the level of quarks) and hence the particles always appear in pairs or in triples.
[Edited on 24-10-16 by woelen]
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blogfast25
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Re. magnetism, it might be useful to draw an analogy with gravity and gravitational potential energy.
Two bodies of masses resp. m and M and separated by a distance r exert an attractive force as per Newton:
$$F=\frac{GMm}{r^2}$$
The potential energy of the system is:
$$U(r)=-\frac{GMm}{r}$$
The minus sign may be a little puzzling but it fits. If we want to increase the distance r we need to act against the
attractive force and perform (positive) work:
$$W=\Delta U=-GMm\Big(\frac{1}{r_2}-\frac{1}{r_1}\Big)=GMm\Big(\frac{1}{r_1}-\frac{1}{r_2}\Big)>0$$
Note also that:
$$r\to+\infty \implies U(r)\to 0$$
[Edited on 24-10-2016 by blogfast25]
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blogfast25
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| Quote: Originally posted by woelen |
Nuclear forces fall off much more rapidly. Weak nuclear forces fall off exponentially, the potential can be written as -K*exp(-mr)/r with r being the
distance between the interacting objects, K and m being certain positive constants. The factor exp(-mr) only needs to be taken into account at a scale
of nuclear radii (which is in the order of magnitude of 10000 times as small as atomic radii), so at an atomic scale this force is at the order of
magnitude of 10^(-1000) or so smaller than at nuclear scale. For strong nuclear forces I do not know the rate at which they fall off. These forces do
not really fall off, they are so strong that particles always are close to each other. It simply is not possible to have particles further away for
strong nuclear forces (which act at the level of quarks) and hence the particles always appear in pairs or in triples. |
The much smaller scales of the nuclear forces, compared to electrostatic forces, also has a strong bearing on the confinement energies, as predicted
by QP.
The ground state of hydrogen (its electron cloud) is -13.6 eV.
The measured ground state of a deuteron nucleus is - 2.225 MeV! Over a 100,000 times larger.
That's why in terms of energy density chemical ways of generating energy (like combustion) could never compete with nuclear methods.
[Edited on 24-10-2016 by blogfast25]
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PHILOU Zrealone
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| Quote: Originally posted by Sulaiman | Imagine a universe uniformly consisting of nails stably floating in 'space'.
If you input a little energy to magnetise one of these nails,
all others will be atracted to it .... massive free energy ?
How about if just one extra nail is introduced to the otherwise uniform universe ?
so physical separation is a form of energy
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Gravitational force will already induce aggregation into an iron planet...
For the rest most of the posters here seems to forget that the magnet induces a transformation of the iron nail what starts to be magnetised upon
contact with the magnet (or when in close viccinity if the magnetic field is strong enough).
The change is micro-structural like on a crystalline level...micro-magnetic cell fields that adds and rearrange their "spin" by mutual influence.
I hardly think that this happens without energy change of the system (magnet, iron nail and surrounding).
[Edited on 27-11-2016 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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