Physics

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Originally posted by russ_watters


Why? the change in your pocket doesn't end up as a solid mass of metal, does it? Metal objects need to be chemically bonded together to become one object (a weld is chemical bonds).

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No, I was talking about pure metals (without oxide or other things on the surface) in a vaccum chamber. Since the metal atoms can form bonds easily, I think it is possible for two metal objects to become one under room temperature. It is much easier under high temperature (that's how we weld metals).

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No, I was talking about pure metals (without oxide or other things on the surface) in a vaccum chamber. Since the metal atoms can form bonds easily, I think it is possible for two metal objects to become one under room temperature. It is much easier under high temperature (that's how we weld metals).

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A brand new penny has very little oxidation and air doesn't make any difference since there will always be places where there is no air between the pennies (otherwise they woudln't jingle). And yes, the bonds are easy to form, but not so easy that they form sponatneously. They need a push - force or heat.

OK, you seem to be saying that all solids are held together by chemical bonds, right? That would explain it, but I guess I don't see why that is. Is it somehow related to that "heat of fusion" stuff? Wait, nevermind..that is going the wrong way. (takes heat to *melt* it, so it gives off heat when it freezes)

I was under the impression that the only difference between solids and liquids was that liquid molecules had enough energy to freely move past one another, and solids do not. But the intermolecular forces involved would be exactly the same.

Anyway, that's what's going on in my mind. Am I making myself look like an idiot? ;)

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Originally posted by pcchen


No, I was talking about pure metals (without oxide or other things on the surface) in a vaccum chamber. Since the metal atoms can form bonds easily, I think it is possible for two metal objects to become one under room temperature. It is much easier under high temperature (that's how we weld metals).

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I don’t believe the atoms at the surface would just “sit” in a state ready to fuse with another piece of metal even in a vacuum where there would be no way of oxidization, etc on the surface. The surface atoms would not have a complete complement of electrons in their outer shell, this is just about the least favorite state there could be, so I’m certain they would find a way to complete their shell. Once this occurred, there would be an energy barrier to overcome before the two pieces fused as you suggest. Gravity alone would not be able to overcome this.

No, I don't know what happens if you just put two objects together. However, I believe that you don't need too much force to make two metal objects to become one. Some information about "cold welding" may be interesting (although I can't find much on google). However, cole welding works only on some types of metal...

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Originally posted by Strogian
Two separated liquids of the same material will combine without any chemical bonds, right? So what makes solids different? Take water for example. If you take two ice cubes and put them together, they don't bond. But if you melt them down (just a layer of liquid on the surface may suffice) and refreeze them, they've become a single object. There aren't any chemical reactions going on there, right? What was preventing them from bonding when solid?

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Actually chemical bonds do occur. The bonds between water molecules are called hydrogen bonds. Because the oxygen molecule is more electronegative (wants electrons really bad) compared to hydrogen the oxygen atom actually starts to draw hydrogens' electrons closer to itself. This causes oxygen to be slightly negatively charged and hydrogen slightly positively charged. Because H20 molecules have this small charge they actually bond to each other (hydrogen atom to an oxygen atom of another molecule and vice versa.) This is why water forms droplets. *edit* my ASCII diagrams didn't format correctly so you might want to do a search for hydrogen bonding in google to get some nice pictures.

Ice forms when these water is frozen into a crystal lattice; the molecules align themselves with their neighbors so that the oxygen of one molecule is near a hydrogen of another. When this happens the molecules actually spread out. This is why ice floats on water, not because there are air bubbles in the ice. Two ice blocks don't bond togeather because their crystal lattices have not made any connections.

Hydrogen bonding occurs when hydrogen is bound to highly electronegative atoms such as nitrogen, fluorine, and oxygen. This is not the only type of bonding that occurs between molecules. There is something called London Dispersion Forces, too. I won't get into that but you can do a search for Intermolecular Forces (IMFs) in google to learn more and get diagrams which will explain a whole lot.

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Originally posted by mozilla4

Actually chemical bonds do occur. The bonds between water molecules are called hydrogen bonds. Because the oxygen molecule is more electronegative (wants electrons really bad) compared to hydrogen the oxygen atom actually starts to draw hydrogens' electrons closer to itself. This causes oxygen to be slightly negatively charged and hydrogen slightly positively charged. Because H20 molecules have this small charge they actually bond to each other (hydrogen atom to an oxygen atom of another molecule and vice versa.) This is why water forms droplets. *edit* my ASCII diagrams didn't format correctly so you might want to do a search for hydrogen bonding in google to get some nice pictures.

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What do you do for living mozilaa? I am just wondering you have all this chemistry knowledge for business or pleasure?

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Originally posted by Prince
What do you do for living mozilaa? I am just wondering you have all this chemistry knowledge for business or pleasure?

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I do chemistry research for business. I work for Smith's Chemistry Corporation a wholly owned subsidiary of The College Board. ;) :D

Just thought of another question, regarding the speed of light. (what this topic was originally about, I think ;)) If the speed of light is measured in a vacuum, I know that it is always measured to be c, regardless of the velocity of the measuring platform. But, if it is measured in some other medium (air, glass, etc.), will the measurement depend on, say, the velocity of the medium? (i.e. if it is windy, will you measure light to be moving more quickly in the direction of the wind?) Or is it still measured as a constant, just less than c?

Light will travel slower in other mediums, but never faster then it travels in a vacuum. The speed is still not dependant on the motion of the underlying medium.

Hmm... what if some winds change the density of air? Doesn't light travel slower in more dense air?