171
votes
Accepted
Why can I touch aluminum foil in the oven and not get burned?
You get burned because energy is transferred from the hot object to your hand until they are both at the same temperature. The more energy transferred, the more damage done to you.
Aluminium, like ...
- 30.8k
140
votes
Accepted
If I pull a metal bar for long enough with a constant small force, will it eventually break?
Yes, the rod will ultimately break—barring any other failure mechanism that occurs first.
(Depending on the material and conditions, you may need to wait a very, very long time, but your mentions of &...
- 27k
132
votes
Why do metals only glow red, yellow and white and not through the full range of the spectrum?
The physics of why the heated metal glows like a black body has already
been thoroughly covered in the previous answers. However, in order to
completely bridge the gap with the physiology of color ...
- 2,271
125
votes
Why can I touch aluminum foil in the oven and not get burned?
While it's true that the difference in specific heat capacity is to your advantage, its effect is really dwarfed by the mass difference. Typical aluminium foil is 0.016 mm thick and weighs 0.043 kg/m²,...
- 4,819
45
votes
Are there physical properties that can be used to differentiate stainless steel from copper in a home environment?
Take advantage of the large difference in thermal conductivity between copper and stainless steel (approximately $400$ and $16$ $\mathrm{Wm^{-1}K^{-1}}$ respectively). If you put one end of a metal ...
- 6,186
43
votes
Accepted
Why do metals have free electrons?
Without getting into the quantum mechanical details, here’s a cartoon depiction of what’s going on. The vertical axis represents energy.
Like other answers have already pointed out, metals don’t have ...
- 9,468
40
votes
How can electric fields be used to detect cracks in metals?
Cracks and other flaws can be found in metal parts by scanning the surface of the part with a small electromagnetic coil, which induces a current flow in the metal part as if the coil and the part ...
- 96.6k
39
votes
Why do metals only glow red, yellow and white and not through the full range of the spectrum?
When metals (or any materials) get very hot, they emit "black body radiation". It's a funny name, because even "non black" bodies emit this thermal radiation. There may be some (small) deviations from ...
- 119k
31
votes
Are there physical properties that can be used to differentiate stainless steel from copper in a home environment?
Why not density? At least for a quick check and as for the title question. You are dealing with about < 8 and 9 g per cubic cm, respectively for steel and copper.
Not overly laborious and ...
- 1,729
29
votes
If I pull a metal bar for long enough with a constant small force, will it eventually break?
This paper describes scientific creep tests with some specific steel.
In a low stress (but relatively high temperature) regime, they report creep of 200 micrometers per year, for a test specimen of ...
- 2,757
27
votes
How is silver a better conductor than platinum?
The situation is a lot more complicated than you described. When calculating the conductance of a metal, you first need to evaluate the allowed energy states of electrons in the bulk material, which ...
- 10.4k
23
votes
Why do metals only glow red, yellow and white and not through the full range of the spectrum?
When I refer to a colour, eg green, I an referring to a range of wavelength which on entering the eye are perceived to be a range of colours depending on the intensity of each of the wavelengths ...
- 98.6k
22
votes
Accepted
Platinum seems to have higher kinetic friction coef. than static - how is this possible?
If you check the references in the Wikipedia article you linked, you will see that the source for the kinetic is different from the source for the static coefficient of the metals your mention (...
- 15.4k
18
votes
Can electrons absorb photons?
Bottom line up front: You don't get absorption phenomena with a single free electron. You need to look at a system such as an atom or a crystal, in which there are more complicated dynamics at play ...
- 52.1k
17
votes
Are there physical properties that can be used to differentiate stainless steel from copper in a home environment?
What about Eddy currents? If you've got a pair of strong neodymium magnets (doesn't everyone?) - move the straw in between two magnets with their poles opposing. Copper/Aluminum will have a strong ...
- 171
17
votes
Accepted
Is the specular reflection on a polished gold sphere white or gold in colour?
Yes, specular reflection from polished gold is gold colored. Due to the interband transition in gold, green and blue light gets strongly absorbed, biasing the reflected spectrum toward yellow and red. ...
- 12k
16
votes
Are there physical properties that can be used to differentiate stainless steel from copper in a home environment?
To see if the straw is stainless steel with a copper-colored coating, you can carefully sand or file off a bit of material from the end of the straw and see whether or not it is copper-colored ...
- 96.6k
16
votes
Accepted
Why do group II elements conduct?
Even when an isolated atom has a filled shell, the electron bands in a solid crystal may be partially filled. The reason is that bands that originate from different atomic orbitals may actually ...
Buzz♦
- 16.5k
14
votes
How is silver a better conductor than platinum?
It appears that none of the responses so far have addressed the real reason silver is a better conductor than platinum.
The reason is electron scattering. The simplest model for conductivity in solid ...
- 12k
13
votes
Accepted
Why can't the charge carriers leave the conductor?
Fundamentally they can't leave because they are attracted to the fixed positively charged atomic nuclei in the material.
This results in the work function, meaning an amount of energy required to free ...
- 28.7k
12
votes
Why do metals only glow red, yellow and white and not through the full range of the spectrum?
All wavelengths are included in what you call "white", thus all wavelengths are there.
The evolution you are describing is the evolution of the black body radiation as heat is increased.
You can ...
- 235k
12
votes
How is silver a better conductor than platinum?
I'll add my two cents to the other answers from the audio perspective that hopefully would clarify the "platinum cable" issue.
First of all, there is a belief in the audio field that an ideal ...
- 12.7k
12
votes
Can you make a metal denser by melting it and make it cool down under high pressure?
First of all, high pressure (i.e., compressive equitriaxial stress) is simply not going to induce cracks (or failure of any sort) in a uniform solid—there's just nowhere for the material to move to ...
- 27k
11
votes
Accepted
Why the electrons below the Fermi level do not conduct electricity?
Electrons in Solids
Electrons in solids are treated by the so-called Band Theory, a quantum mechanical model for fermions interacting with a fixed crystal lattice. The solution to the Schrodinger's ...
- 17.9k
11
votes
Accepted
Why are metals malleable and ductile?
Let's draw a comparison with ceramics, which—just as metals are generally ductile—are generally brittle.
First, note that crystals (and metals and ceramics are both generally polycrystalline) can ...
- 27k
11
votes
Why can I touch aluminum foil in the oven and not get burned?
What's in discussion here is specific heat capacity. The flow of heat is based around temperature, and whilst that may seem like a fairly obvious statement, there are important distinctions to be made ...
- 972
11
votes
Why can I touch aluminum foil in the oven and not get burned?
There are three categories of heat transfers:
Convection and radiation transfers happen over the whole area (both sides!) of the aluminum foil while the conduction only happens over the area touched ...
- 1,897
11
votes
If I pull a metal bar for long enough with a constant small force, will it eventually break?
Under normal conditions structure building materials, such as steel, will not yield or break. Which is good, because all modern buildings and bridges are based on steel, even if embedded in the ...
- 16.8k
10
votes
Are there published predictions that hydrogen could remain metallic at ambient pressure?
According to http://iopscience.iop.org/article/10.1088/1742-6596/215/1/012194/pdf, "Brovman, Kagan, and Kholas[5] showed that hydrogen would be a metastable metal with a potential barrier of ~1 ...
- 27.1k
9
votes
If I pull a metal bar for long enough with a constant small force, will it eventually break?
What matters here much more than force is stress:
$$\sigma=\frac{F}{A_0}$$
where $F$ is the force applied to a bar with cross-section $A_0$.
and the strain:
$$\varepsilon=\frac{L-L_0}{L_0}$$
The ...
- 35.4k
Only top scored, non community-wiki answers of a minimum length are eligible