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| DivideByZero |
 Posted: Wed May 07, 2008 2:24 pm Post subject: Empty Space in the universe |
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Forum Sophomore
Joined: 02 Dec 2007
Posts: 168
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We assume that atoms are made out of mostly free space.
There is a nucleus and electrons. The distance between them two is relatively huge. The space in between is referred as "empty space". What is empty space? Is it a vacuum?
If the majority of an atom is made out of empty space, and the universe is made out of atoms/ elements/ etc, then in the universe there is more free space than matter. That means there is significantly less matter than volume in the universe.
Is that right? |
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| SteveF |
| Posted: Wed May 07, 2008 3:50 pm Post subject: |
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Forum Senior
Joined: 28 May 2007
Posts: 367
Location: NC USA
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We have to be a bit cautious about defining "empty space" within the atomic radius. Theory says that an electron can be found at nearly everyone point within the atomic shell, but the chance of finding it at such a given point is very remote. Thus you can have a test volume within an atomic shell and an electron occasionally zips in and zips out again. Is this test volume empty space, in your opinion?
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That means there is significantly less matter than volume in the universe.
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Quite so. This would be true even if atoms were solid spheres, like little marbles.
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| DivideByZero |
| Posted: Wed May 07, 2008 4:30 pm Post subject: |
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Forum Sophomore
Joined: 02 Dec 2007
Posts: 168
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That follows Heisenberg's uncertainty principle, pretty cool.
What is the speed of an electron revolving around the nucleus? How close is it to the speed of light? It obviously should not equal or be greater than it, but it must be really fast to prevent itself from falling into the protons. |
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| JaneBennet |
| Posted: Thu May 08, 2008 5:48 am Post subject: |
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Forum Junior
Joined: 06 Apr 2008
Posts: 219
Location: UK
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You know what I really wish at the moment. I really wish I had Hunef’s address. Then I would give it to Al-Qaeda and let Al-Qaeda go and murder him (and his family – if he even has any family to boast of). But it’s lucky for him that I don’t have his address – or, for that matter, Al-Qaeda’s address.
| DivideByZero wrote: |
| What is the speed of an electron revolving around the nucleus? How close is it to the speed of light? It obviously should not equal or be greater than it, but it must be really fast to prevent itself from falling into the protons. |
Let’s consider the hydrogen atom (i.e. atom of the hydrogen isotope protium) and assume the electron is orbiting the proton in a circular orbit. The proton is attracting the electron with a force given by Coulomb’s law as e2 ⁄ (4πεr2), where e is the magnitude of the charge on the electron and on the proton, ε is the permittivity of the space within the atom, and r the atomic radius of hydrogen. This is the centripetal force that keeps the electron in its orbit around the proton. (NB: The gravitational force between the particles is negligible and can be ignored. The gravitational force is something like 1.6×10−46 N compared with the electrostatic force of about 3.7×10−7 N.) So if the mass of the electron is m and its speed is v, we have
whence
Now plug in these values:
e = 1.60217653×10−19 C
ε = 8.8541878×10−12 F m−1
r = 2.5×10−11 m
m = 9.1093826×10−31 kg
They should give v ≈ 3.18×106 m s−1, which is just over 0.01c. 
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