The study of how the properties of matter arise from its structure at all scales and of how processing can be used to modify those properties (often in pursuit of a specific application).
23
votes
8answers
8k 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?
19
votes
3answers
553 views
Why wet is dark?
When something gets wet, it usually appears darker. This can be observed with soil, sand, cloth, paper, concrete, bricks ...
What is the reason for this? How does water soaking into the material ...
18
votes
1answer
455 views
Why is tape so hard to rip when it is not broken, but so easy once there is the tiniest cut in it?
Question says it all. Ripping a piece of tape along the width is tough, stretches the tape, messes it up, etc, but if you put the tiniest nick at the top, it rips without any problems. Why is that?
13
votes
3answers
2k views
Roughly how many atoms thick is the layer of graphite left by a pencil writing on paper?
Actually I can't expand much as the question pretty much explains the query. I would be interested in the method of estimating an answer as well as a potential way to measure it experimentally. ...
11
votes
3answers
615 views
Is one way glass possible?
I am not talking about mirrors, just a plain window made of glass like material. Would it be possible to allow light pass only in one direction but not the other?
11
votes
3answers
414 views
Why are materials that are better at conducting electricity also proportionately better at conducting heat?
It seems like among the electrical conductors there's a relationship between the ability to conduct heat as well as electricity. Eg: Copper is better than aluminum at conducting both electricity and ...
11
votes
3answers
1k views
How does paper make sound when it is torn?
We know that from our experience when we tear up a piece of paper, we can hear a characteristic sound. What is the underlying mechanism behind it? What do the dominant frequencies (edit: I don't mean ...
9
votes
1answer
783 views
Why does paper become transparent when smeared with oil but not (so much) with water?
When I smear oil onto a scrap of paper and rub it in, the paper becomes quite transparent; but when I attempt the same with water it doesn't as much. Why?
8
votes
3answers
2k views
Why can one bend glass fiber?
Why can one bend glass fibers without breaking it, whereas glasses one comes across in real life is usually solid?
Is there also a good high-school level explanation of this?
8
votes
3answers
1k views
What determines the color of a pure substance and is it possible to predict it?
I have always wondered why salt is white, water is clear and gold is, well, gold. What determines the color of a substance? Does it have something to do with the electrons? And is it possible to ...
8
votes
2answers
181 views
Shape of wall's deformation wave caused by baseball's impact
Clicking through this year's top sports pictures, I stumbled upon this one. I was wondering about the shape the baseball is leaving on the wall.
What phenomenon causes this peculiar shape? Why is ...
7
votes
2answers
218 views
Why is paper more frangible when it is wet?
My four-year-old daughter asked me why paper tends to fall apart when wet, and I wasn't sure. I speculated that the water lubricates the paper fibers so that they can untangle and separate more ...
7
votes
2answers
173 views
Ferromagnetism with mobile spins
How can electron spins in Iron at room temperature have ferromagnetic order even though they are travelling at very high speeds?
One could argue that spin and motion are completely uncorrelated and ...
7
votes
3answers
743 views
Why will clay, when heated to high temperatures, harden and become waterproof?
I have a question
Why will clay, when heated to high temperatures, harden and become waterproof?
7
votes
1answer
261 views
Force curve associated with squeezing a worm-like chain (WLC) between two parallel plates
Let's say I have a polymer, of contour length $L_p$ and persistence length $P$, positioned between two parallel plates separated by a distance $z$. I slowly squeeze the plates together until only ...
6
votes
2answers
413 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
925 views
Why are some materials diamagnetic, others paramagnetic, and others ferromagnetic?
Why are some materials diamagnetic, others paramagnetic, and others ferromagnetic?
Or, put another way, which of their atomic properties determines which of the three forms of magnetism (if at all) ...
6
votes
1answer
738 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
2answers
269 views
How does infrared light 'erase' phosphorescence on zinc sulfide?
I found some sheets of zinc sulfide in my basement that phosphoresce green for up to 24 hours or so after exposure to bright light in the violet range or shorter. One of the first things I tried was ...
5
votes
2answers
6k 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 ...
5
votes
2answers
128 views
In mechanics, is shock really better expressed as jerk instead of acceleration?
Some expensive electronics or mechanical devices are designed to be shock-resistant. However, the manufacturers often market the level of shock-resistance in units of g-force (I know g-force is really ...
5
votes
1answer
806 views
Transparency of materials
Is transparency of material has something to do with inter- or intra-molecular bonding? E.g. both graphite and diamond are carbon, but graphite is opaque and diamond transparent.
4
votes
4answers
3k views
Does glass get stronger the longer its under water?
I was reading the internets and I saw an image of of random facts. Yes, I know, its a humor site, but based on the image item #23 I have some questions.
Does glass really get stronger the longer its ...
4
votes
2answers
138 views
Graphene +1 extra carbon bond
I'm not a physicist just a curious mind, so please go easy!
I was just watching a BBC Horizon Documentary that featured a piece on the recently discovered material Graphene. One of the facts ...
4
votes
2answers
155 views
What properties would the ideal material for spacecraft construction possess?
Assuming we develop the capability to send a robot to study Gliese 518, or any of the Earth-like planets discovered in the neighbourhood; the spacecraft would need to travel through the Solar System ...
4
votes
1answer
949 views
How to know what materials are good conductors of electricity?
I'm not asking a question like "Is the wood conductive?". No. I'm asking what properties do they have to have to be good conductors. Theoretically I mean. Thanks.
4
votes
2answers
249 views
How to calculate the highest theoretical artificial hill?
The biggest peak in the world is Mount Everest.
Imagine someone starting to make an artificial hill (like pyramide) from soil (earth).
So, when starting with an 200x200 Km base area, with 45degree ...
4
votes
1answer
429 views
BCS theory, Richardson model and Superconductivity
I'm studying Richardson Model in second quantization. There are many initial points that I don't understand:
We supposed that an attractive force between 2 electrons exists, due to electron-phonon ...
4
votes
1answer
60 views
Thermal conductivity affected by electrical current
Does anyone know of any materials whereby the thermal conductivity can be changed by passing an electrical current through the material?
4
votes
1answer
77 views
limits of diamond anvils for high pressure research
in this wikipedia article regarding diamond anvils, it mentions that the pressure peaks roughly at 300 GPa.
My question is why is this so? is the diamond crystal structure collapsing if higher ...
4
votes
1answer
536 views
Physical meaning of elastic constants of a monoclinic crystal
For the elasticity of a material, Hook's law can be written in tensorial form as:
$$\sigma = \mathsf{C}\, \varepsilon$$
where $\sigma$ is the Cauchy stress tensor, $\varepsilon$ is the infinitesimal ...
4
votes
2answers
225 views
Do amorphous metals undergo conchoidal fracture?
Amorphous metals are often referred to as metallic glasses due to their quenched atomic disorder. Do they fracture in the same fashion as silicate glasses? If not, what failure mode(s) do they have?
4
votes
2answers
744 views
Stress tensor in a cube with shear forces
I want to calculate stress matrix in a cube with two faces parallel to x axis and perpendicular to z axis (sorry I don't know how can I put a picture in this post).
There are two force uniform ...
4
votes
0answers
41 views
Order of magnetic phase transitions
Is there any phase transition occur in paramagnetism to diamagnetism transitions state. What should be the order and how will I calculate the order?
4
votes
0answers
94 views
Why does the overhand knot jam but the figure-8 knot doesn't?
After tensioning a rope with an overhand knot in it, it is often very hard if not impossible to untie it; a figure-8 knot, on the other hand, still releases easily.
Why is that so? Most "knot and ...
4
votes
0answers
776 views
Inflating a balloon (expansion resistance)
I am doing a quick calculation on how to calculate the pressure needed to inflate a perfectly spherical balloon to a certain volume, however I have difficulties with the fact that the balloon (rubber) ...
3
votes
1answer
208 views
Why does glass break at the line where you score it?
Why does it take such a small incision for the glass to break at that spot? Why is the structural strength of the material influenced by such a small imperfection?
3
votes
2answers
232 views
Consequences of destroying a space elevator
Suppose there is a fully functional space elevator built on Earth. The base is attached to coordinates
$
(\lambda, \varphi) = (0,0)
$
e.g., on the equator on the zero-meridian.
What would happen ...
3
votes
3answers
625 views
Optimal technique to tear perforated paper along the perforation [closed]
My daughter's coloring book has perforated pages, so you can easily rip out the pages for easier coloring action. Great.
Trouble is, the perforation isn't enough, and it's almost impossible to rip ...
3
votes
3answers
894 views
Which metals can cause magnetic interference (passively)?
I am developing an application that uses the magnetometer inside smart-phones to detect orientation w.r.t. the Earth's magnetic field.
I have noticed that when the phone is held close to a metal ...
3
votes
4answers
144 views
Effects of surface roughness on specularity
Say you have a piece of glass, which looks specular if propery cut/polished. But if you sand the surface using say sand paper, it will look hazy and glossy. I'm wondering how much surface roughness ...
3
votes
3answers
268 views
Why is copper diamagnetic?
Cu has an unpaired electron in 4s, but it is diamagnetic. I thought that it has to be paramagnetic. What am I missing?
3
votes
2answers
255 views
How is the stickiness of a fluid measured?
How does one compare the "stickiness" of different substances on a certain surface?
For example:
Does glue A stick better to steel than glue B?
Does water stick better to steel than oil?
3
votes
1answer
191 views
Why do non-stick frying pans work?
Modern non-stick frying pans use a mixture of titanium and ceramic that is sandblasted onto the pan surface, and then fired to 2,000 °C (according to Wikipedia).
Can anyone explain (at the molecular ...
3
votes
4answers
2k views
Graphene space elevator possible?
I just read this story on MIT working on industrial scale, km^2 sheet production of graphene.
A quick check of Wikipedia on graphene and Wikipedia on space elevator tells me
Measurements have ...
3
votes
1answer
106 views
What states of matter are possible at lowest temperature?
Near absolute zero, some materials are superconductors. Other materials are superfluids. Others are Bose-Einstein Condensates.
Is there a complete list of possibilities? Or is this still a research ...
3
votes
1answer
538 views
Why can glass absorb ultraviolet light?
Please see the following photos. (I cannot post them...)
http://i1163.photobucket.com/albums/q554/startanewww/CIMG4545.jpg
http://i1163.photobucket.com/albums/q554/startanewww/CIMG4546.jpg
From the ...
3
votes
1answer
222 views
How much does a steel spring wire bend due to it's own weight?
I'm working on an art project and I need to know how much a steel spring wire bends dependent on it's diameter. It's point of support is in the middle and it's lengths is ...
3
votes
1answer
522 views
Penetration of armor plate
Is there a simple mathematical expression for the stopping power of a given thickness of armor, given the thickness of armor plate, the radius of a cannon ball, the density of the cannonball and the ...
3
votes
1answer
239 views
Is there any way to increase a rubber-bands lifetime?
Rubber-bands are simple, yet very useful. Old rubber bands(5 years?) get brittle? Why is that?
