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205
votes
11answers
44k views

Why don't metals bond when touched together?

It is my understanding that metals are a crystal lattice of ions, held together by delocalized electrons, which move freely through the lattice (and conduct electricity, heat, etc.). If two pieces ...
71
votes
6answers
19k views

Why are most metals gray/silver?

Why do most metals (iron, tin, aluminum, lead, zinc, tungsten, nickel, etc.) appear silver or gray in color? (What atomic characteristics determine the color?) What makes copper and gold have ...
46
votes
8answers
55k views

Will a hole cut into a metal disk expand or shrink when the disc is heated?

Suppose you take a metal disc and cut a small, circular hole in the center. When you heat the whole thing, will the hole's diameter increase or decrease? and why?
45
votes
2answers
6k views

Why are gold mirrors yellow?

Why are golden mirrors yellow? Do they add a yellow component to the spectrum or absorb non-yellow components? If they absorb, then why are they used in telescopes being imperfect? If they add a ...
35
votes
1answer
6k views

Was Titanic's captain's decision correct?

I just saw a documentary on Titanic. Someone in that documentary told Captain Smith "Shall we close the water tight doors, sir?" and the Captain replied "No, let it be open. Let the water ...
23
votes
3answers
27k views

Is there a compound denser than the densest element?

I'm musing about how to give students an intuitive feeling about density by letting them lift a same sized volume of different materials, e.g. 1 liter of water, a 10x10x10 cm cube of iron, lead etc. ...
21
votes
2answers
2k views

Why don't free electrons fall from metals if shaken?

This is a question we were asked at a physics lecture.
17
votes
1answer
294 views

Third-order susceptibilities of metals?

Can anyone point me to a source for measurements of the third-order nonlinear electric susceptibilities $\chi^{(3)}$ of various metals? Specifically in relation to the AC Kerr effect, so measurements ...
16
votes
1answer
3k views

When heat is applied to the top of a stack of pennies, why does the bottom penny melt first?

I just watched this video where a blow torch is used on the top of a stack of pennies. I'd like to know why the bottom penny melted first.
15
votes
3answers
823 views

Why would different metals glow red at different temperatures?

According to everything I've been taught about incandescence and black-body radiation, and some quick Googling to confirm I'm not crazy, just about everything, regardless of composition, should start ...
12
votes
1answer
2k views

Resistance between two points in an infinite metal sphere/cube

Let's imagine that we have a tridimensional metal object of infinite size, and decide to calculate the resistance between two arbitrary points. How would we go about doing this? I have thought of two ...
10
votes
3answers
40k views

Hollow Tube Stronger than Solid bar of same Outside Diameter (O.D.)?

I was listening to some co-workers talking about problems meeting stiffness requirements. Someone said that even with a solid metal rod (instead of the existing tube) we could not meet stiffness ...
10
votes
1answer
443 views

Why aren't superconductors shiny? [duplicate]

Superconductors are really good at conducting electricity. Should they not reflect light very well too?
9
votes
3answers
38k views

In electrostatics, why the electric field inside a conductor is zero?

In electromagnetism books, such as Griffiths or the like, when they talk about the properties of conductors in case of electrostatics they say that the electric field inside a conductor is zero. I ...
9
votes
3answers
399 views

Why are permanent magnets permanent?

Let me see if I get it right. When an iron bar is attracted by a permanent magnet it becomes a magnet itself because all of its magnetic domains start to point in the same direction. When the iron bar ...
8
votes
2answers
891 views

Why does Platinum evaporate if left long enough?

I have been reading into research relating to the redefining the 1 kg weight as the current Platinum-Iridium is becoming smaller. In this article, here, it mentions that the original metal weight ...
7
votes
4answers
5k views

How does positive charge spread out in conductors?

I know that when there are excess positive charges in a conductor, for example, a metal sphere, the positive charges will spread out over its surface. However, I am confused about how this excess ...
7
votes
2answers
32k views

Why does magnet attract iron but not other metals?

While searching, i found this page: http://timesofindia.indiatimes.com/home/stoi/Why-does-a-magnet-attract-iron/articleshow/4298171.cms but it does not have full explanation. So Please tell full ...
7
votes
2answers
465 views

Can molten metal be suspended in air?

I wondered if magnets could be used to hold a drop of molten liquid metal in air (not for any particular reason just because it could be done), but was disappointed when a quick Google search showed ...
7
votes
2answers
4k views

Why is quicksilver (mercury) liquid at room temperature?

This is a nice question when you find it out, and I am really looking for a proper answer. Take quicksilver (Hg) in the periodic table. It has one proton more than Gold (melting point 1337.33 K), and ...
6
votes
4answers
14k views

Why is the conductor an equipotential surface in electrostatics?

Since the electric field inside a conductor is zero that means the potential is constant inside a conductor, which means the "inside" of a conductor is an equal potential region. Why do books also ...
6
votes
1answer
9k views

What tests can I do at home to identify any metal?

Regarding a question on another Stack Exchange site which identifies a weighted Lego brick to be some kind of metal, I wanted to know how to identify a metal, perhaps limited to household objects like ...
6
votes
3answers
7k views

How hot can metal get in sunlight? [closed]

I will make some 5mm blackened steel letters for a building. Now, in the sunlight in summer, how hot can they get? EDIT: i want to place some LEDs on the back of the letters. now the question is if ...
6
votes
1answer
250 views

Reflectivity of a glowing-hot metal surface

When a polished piece of metal (or steel in particular) is heated to incandescence, how do its reflective properties change? Given a mirror-like surface, would the object temporarily cease to act ...
6
votes
2answers
955 views

If sound wave is going to hit any metals can it make that metal electrons into exited state?

What will happen when sound wave hits the metals with very high frequency can it make the electrons to exited state. If it happens then what will be the state of that metal
6
votes
1answer
60 views

What happens at the point of welding iron?

What is the physics behind welding iron? It is obviously the electricity that causes the two metal parts to fuse but what is the role of the welding rod and why is it said to damage your eyes when you ...
6
votes
1answer
2k views

What is the penetration length of static electric field into conducting metals?

How large is the penetration length for static electric field into good conductors? I have two versions: (1) few atomic spacings $$a\sim n_{e}^{-1/3},$$ and (2) Debye length computed by Fermi ...
5
votes
1answer
1k views

Why does a gold leaf appear blue if made very thin?

Is this to do with excitation of electrons and emission of photons? Or is it more to do with the structure of the gold I.e. Only small wavelengths being able to pass through gaps between atoms? EDIT: ...
5
votes
1answer
2k views

Why do most metals appear silver in color with gold being an exception from a scattering and EM viewpoint?

Related: Why are most metals gray/silver? After reading Johannes’ impressive answer to Ali Abbasinasab question of why do most metals appear silver in color with the exception of gold (and copper), ...
5
votes
3answers
654 views

Why do magnets silence anvils?

Today I've been to a forge. The blacksmith demonstrated that if he beats the anvil without a magnet attached, it make horrible noises. As soon as he reattached it, the sound of the anvil was way more ...
5
votes
1answer
170 views

Why does aluminium-on-glass mirror work without distortion?

I have read an article about glass (zerodur) with low thermal expansion coefficient. It is mentioned that large casts of such glass are covered with reflective layer of Aluminium and used as mirrors ...
5
votes
2answers
4k views

Could airport security possibly distinguish gold and silver coins from other coins?

People usually don't carry pure gold and silver coins in their wallets. If I put some in my wallet, would it be likely that airport security would detect some anomaly with my wallet as compared to ...
4
votes
2answers
113 views

Metal Dilemma: Only very few civilizations per galaxy

This is a question in the area of extraterrestrial life. While life may be possible without it, space travel is probably impossible without metal. Metal is created in stars and heavy metals (above ...
4
votes
3answers
219 views

What happens to the electrons when metal gets cut or broken?

For example, if I take an iron rod (or thread) and cut it in half, could it happen that one side remains with an extra electron or would it balance out too fast? If possible, do the parts simply ...
4
votes
4answers
236 views

If you suddenly move a piece of metal, will that disturb the free electron density?

If we have a hollow pipe sitting at rest filled with gas and we moved the pipe suddenly along its length to the right, then the gas density will be momentarily higher near the rear of the pipe and ...
4
votes
1answer
167 views

Reflection, Transmission, and Plasma Frequency

Does anyone have a good, clear explanation of why and how this works? I don't understand the following. Say you have a piece of metal with a plasma frequency $\omega_p$. This is like a resonant ...
4
votes
2answers
28k views

Why is stainless steel a poor conductor of electricity?

I recently had a metal plate put in my shoulder and was wondering why stainless steel isn't a good conductor (At least I hope it isn't). Does the alloy just lack free electrons? Why is that?
4
votes
1answer
85 views

Resources in space, and their distribution

I'm making a video game in which the economics of an interstellar civilization is important. What I'm wondering is, how are resources in space distributed? Since everything ultimately comes from ...
4
votes
2answers
350 views

What is the most efficient way to use a blow torch?

Let's start with a torch and a piece of titanium. What is the fastest way to get the titanium up to red hot? Whenever I ask my science-y friends they like to point out that the bright blue tip is ...
4
votes
1answer
60 views

Temperature effects on lead against radiation

I would like to know if bringing lead to near absolute zero temperatures would have any affects on how resistive it is against gamma radiation. It takes 40 centimeters of lead to reduce gamma ...
4
votes
1answer
292 views

Why do cold metal plate make less noise?

I have a metal gate in my home so I have noticed that when it is a hot day and if I hit it it makes a lot of noise but when there is a rainy day and the weather and the gate re cold and if I hit the ...
4
votes
1answer
85 views

materials that repel positrons?

In this article is discussed at some length positron formation in metallic surfaces. Positrons have work functions that describe how much energy they have to receive in order to be extracted from the ...
4
votes
2answers
349 views

Is there any relation between temperature dependence of resistance and fermi energy in metals?

Given that the resistance varies linearly with temperature in metals, is there any way we can calculate the Fermi energy from this information?
3
votes
2answers
686 views

X-ray diffraction from Metals

Is X-ray crystallography is possible for metals? Or not due to absorption?
3
votes
2answers
8k views

Will the hole on a metal disc expand or contract upon heating? [duplicate]

Possible Duplicate: Will a hole cut into a metal disk expand or shrink when the disc is heated? The metal disc of diameter D1 has a hole in it and the diameter of the hole is D2 (D2 Now, if I ...
3
votes
2answers
19k views

Are all metals good conductor of electricity?

I am writing an article for kids, which is on conductors and insulators of electricity. If I make a statement that "All metals are electrical conductors and all non-metals are electrical insulators" ...
3
votes
2answers
56 views

Why are metals worse conductors when heated?

When metals, (such as in circuits), are heated, their ability to conduct electric current is hampered. Why is this? Does the transition towards liquid disrupt a metal's ability to conduct, or is ...
3
votes
1answer
113 views

Why are some elemental materials grey?

How does grey occur in elemental materials such as metals? I believe that grey arises from the simultaneous reflection and absorption of all colors of the spectrum (in different atoms of course), as ...
3
votes
1answer
32 views

What are the effects of compositional changes in a thermocouple's junction?

We use thermocouples (type B) to measure the temperature of metals (Fe, Ag, Pd, etc) in a furnace under pressure. We weld two thermocouple wires together using an arc welder. This junction then comes ...
3
votes
1answer
80 views

What happens to the electron density in a metal during an electric discharge?

Suppose we are able to see into a grain of metal at the boundary between the grain and air (perhaps along one of the faces of this cube): (Source: Wikimedia Commons.) This image does not show the ...