# Science questions not worth a thread I: I'm a moron!

Discussion in 'Science & Technology' started by The Imp, May 4, 2010.

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1. ### The ImpKinslayer

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I'll start it off, why doesn't light travel faster or slower then 299 792 458 m/s ?

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It does travel slower. That's the speed of light in a vacuum.

3. ### Gigazcivoholic

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-Maxwells equations demand 299 792 458 m/s propagation speed for electromagnetic waves in a vacuum
-the invariant mass of a photon is zero

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How much energy does a photon have?

If it has no mass does it mean by e = mc^2 it has no energy?

5. ### SouronThe Dark Lord

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ing magnets, how do they work?

7. ### The ImpKinslayer

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Well, I meant can it travel slower in a vacuum unobstructed or faster?

8. ### SouronThe Dark Lord

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The constant nature of speed of light is an observed fact established by the [wiki]Michelson&#8211;Morley experiment[/wiki].

Einstein's theories take that fact as a premise.

9. ### uppiDeity

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E=h*f

h is the Planck's constant and f is the frequency.

That formula is only half of the story. The full formula is:

E^2 = m^2c^4 + p^2c^2

There are two extreme cases. The first is a resting particle. In that case the particle has no momentum (p=0) and thus the formula reduces to E=mc^2. For any particle with a mass greater than zero (and which is not accelerated) it is possible to find the resting frame in which E=mc^2 is valid.

However as photons have no mass, there is no resting frame and and E=mc^2 is not valid. This is the second extreme case of the above formula when a particle has no mass and thus: E=p*c.

with p=h/(2 Pi) * k; k=(2 Pi) / lambda; lambda = c/f you get to E=h*f

10. ### uppiDeity

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Short answer: Electrons have spins, which have a magnetic moment. Usually either the electrons occur in pairs and have opposing spin and cancel each other out, or the spin points in a random direction and the average over many spins results in a magnetic moment close to zero.

But under certain conditions, the spins can align to each other, so that together they have one big magnetic moment. A magnetic moment creates a magnetic field which attracts (or repels, depending on orientation) other magnetic moments.

The long answer would involve a lot of complicated quantum mechanics.

11. ### peter grimes...Retired Moderator

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So, Uppi, does that mean that protons have no magnetic moment, but positrons (the anti-particle mate of electrons) do?

Or do all charged particles (protons & anti-protons, positrons & electrons) have magnetic moments?

And does that mean that neutrons don't have spin?? Or do neutrons have spin, but no magnetic moment?

I'm sure it's easily wiki-able, but I prefer this format

12. ### uppiDeity

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Protons also have a magnetic moment, but they usually don't play a role in ferromagnetism, because the short-range exchange interaction mainly affects electrons, which are far more delocalized than the nucleus.

All charged particles with spin have a magnetic moment.

Neutrons do have spin, and as they are not charged they should have no magnetic moment. But they have a small magneic moment, because it contains charged quarks with spin that have a magnetic moment. As the charge is unevenly distributed among the quarks (-1/3,-1/3 and 2/3) these magnetic moments do not cancel each other out.

13. ### The ImpKinslayer

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Yes, I know this, but why is the speed of light what it is, and can it be faster or slower unobstructed in vacuum?

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Nope. As to why? I'm not really sure that's a sensible question. That's just the way it is.

15. ### The ImpKinslayer

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Forgive me if I am not satisfied with that answer.

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Well my point is not to belittle your question, but to a certain extent remind that every scientific construct has core values that really don't have theoretical justification, they just are that way. Of course, we might postulate something more fundamental, but that too will have said core values.

But I think I should point out that in the case of the speed of light the question isn't so much why the speed of light is 299,792,458 m/s rather why every other speed is X fraction of the speed of light? The speed of light is the most fundamental speed in the universe.

17. ### peter grimes...Retired Moderator

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Are you satisfied with the value of pi? It's the same sort of thing.

18. ### YeekimModeratorModerator

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I really hope I get the English terms right here...

Anyway, symmetrical convex polyhedron, assuming it is made of material with equal and uniform density, should be stable on any of its faces (when placed on flat surface etc).

Now, what is the smallest possible number faces any convex polyhedron (still of uniform density) can be stabilized on? A hunch says me it should be three, but can anyone prove it?

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A polyhedron with curved faces? 2 in that case I reckon (a sphere wouldn't be stable) like a boat shape?

Flat faces - 4 (a tetrahedron).

20. ### YeekimModeratorModerator

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Flat faces.

But I am quite sure it is possible to construct a tetrahedron that can not be stabilized on one of its four faces - that's why I said three...
EDIT: or maybe it's not possible :S

Maybe I was not clear enough: it does not have to be symmetrical any more.