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).

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175
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11answers
36k 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 ...
100
votes
3answers
8k views

How does a knife cut things at the atomic level?

As the title says. It is common sense that sharp things cut, but how do they work at the atomical level?
42
votes
4answers
4k 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 ...
33
votes
8answers
27k 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?
30
votes
2answers
5k views

Is ice a type of glass?

It's kind of a tricky concept I assume, on one side you got those neat shared vertices of SiO2, on the other (water) you don't really have shared vertices, only kinda (but they still want to align ...
21
votes
3answers
4k views

If aerographite is lighter than air, why doesn't it float?

Air is 6 times denser than aerographite but looking at pictures or videos presenting the material, I see it resting on tables rather than raising to the ceiling. Also, since the material is made of ...
21
votes
1answer
760 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?
20
votes
1answer
4k views

Why does paper become translucent 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 translucent; but when I attempt the same with water it doesn't as much. Why?
19
votes
1answer
273 views

How many molecules rub off when I press a key?

I have a lot of questions below but my overarching questions are: Do surfaces rubbing lightly together always strip molecules off of each other? and How can we model that? Clearly the answer to the ...
18
votes
2answers
3k views

Melting diamond and cool down as diamond

Is it possible to melt diamond? And if possible while let it cool will it became diamond again?
18
votes
3answers
3k 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. ...
17
votes
3answers
4k views

Is it possible to avoid the radiation that caused the American flag turned into white on the Moon? [closed]

While lunar images have proven that the American flags planted during the Apollo missions are still standing on the moon, lunar scientists have now said that they probably no longer hold the iconic ...
17
votes
3answers
4k views

Why can't a piece of paper (of non-zero thickness) be folded more than $N$ times?

Updated: In order to fold anything in half, it must be $\pi$ times longer than its thickness, and that depending on how something is folded, the amount its length decreases with each fold differs. ...
15
votes
4answers
2k 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?
14
votes
1answer
2k views

Equation describing magnetic hysteresis

So when you're looking at B-H curves for ferromagnetic substances, you often see these magnetic hysteresis curves, which occur, I gather, largely because of domain formation which has some reversible ...
13
votes
2answers
638 views

How is graphene a 2D substance?

How is graphene a 2D substance? It has length, width and some thickness to it, else it would be invisible. Why is it considered a 2D substance?
13
votes
3answers
296 views

Does extreme cold make **everything** extremely brittle?

First of all, I'm genuinely sorry if this question isn't "serious" enough for this forum! A common cliche in movies and tv is that a very tough object (eg the villain) is frozen, and then hit with ...
13
votes
3answers
2k 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 ...
12
votes
2answers
994 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 ...
12
votes
3answers
1k 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 ...
12
votes
3answers
843 views

Can the speed of light become complex inside a metamaterial?

The speed of light in a material is defined as $c = \frac{1}{\sqrt{\epsilon \mu}}$. There are metamaterials with negative permittivity $\epsilon < 0$ and permeability $\mu < 0$ at the same time. ...
10
votes
3answers
3k 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?
10
votes
3answers
292 views

Are synthetically-produced diamonds as hard as natural diamonds?

I was having a discussion with my friend about the intrinsic worthlessness of diamonds (DeBeers and whatnot) and how synthetic diamonds haven't caught on, again because of the marketing/propoganda ...
10
votes
1answer
204 views

Why does finely cut paper curl?

When paper is cut to a small width, it curls up like this. Why does this happen?
9
votes
3answers
3k 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 ...
9
votes
2answers
240 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 ...
8
votes
3answers
18k 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 ...
8
votes
3answers
354 views

Is an atom-thick sheet of a material visible and tangible?

If one could make a sheet of a material (thickness of an atom), Aluminum for example, would it be visible to naked eyes? What about tangibility? would it be tactile by human finger skin?
8
votes
2answers
259 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
1answer
1k views

physics of wet hair

I'm curious about the physics behind the clumping of wet hair. More specifically, how the amount of water in hair and distance between hairs affect the clumping process. I know intuitively that when ...
7
votes
2answers
563 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 ...
7
votes
2answers
644 views

Is there a Tungsten alloy more dense than gold?

This thought came from researching a previous question. In the spirit of our get-rich-quick scheming I looked up element densities and prices near gold. Element (g/cm^3) (dollars/kg) Uranium ...
7
votes
3answers
1k 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 ...
7
votes
4answers
3k 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
3k 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) ...
7
votes
1answer
320 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
6answers
2k views

Is there any anti-gravity material?

I want to know if there is any anti-gravity material. I am thinking of making flying vehicles which are made up of anti-gravity material so that they will not experience any gravity on them and can ...
6
votes
3answers
196 views

Hollow gold bar

A scammer got a hollow gold bar and fills it with a combination of lead and air, with the same average density as gold. What's the simplest way of discovering the fraud? I know that x-rays will see ...
6
votes
3answers
666 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 ...
6
votes
3answers
146 views

Are there materials that get softer with temperature decrease?

Could be there material that begins melting/softening when it's temperature is lowered? I would say no, but I've seen enough physics to know that not always life is so easy. Moreover I think I've ...
6
votes
1answer
206 views

Why can we skate on ice? [duplicate]

I have known the reason why skate can slide over ice is that water's melting curve in terms of pressure and temperature has a negative slope. If the pressure due to our mass increases sufficiently ...
6
votes
1answer
2k 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.
6
votes
2answers
669 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
129 views

Material implementations of the holographic principle

I'm afraid this question is a little too open-ended, but bear with me while I find a better formulation. carbon allotropes (like fullerenes and graphene) are regular patterned. Conduction bands of ...
6
votes
4answers
382 views

How does water carve rock?

How does water carve rock? And more generally, how does a soft material carve a hard material? Obviously it happens, but is it a continual process (every drop of soft water carries away a minute ...
6
votes
1answer
1k 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 ...
6
votes
0answers
170 views

Why does foam dull knives?

I have recently taken up prop making and just started my first foam-built costume from a video game. These kinds of costume armour builds are often built out of the various foam floor mats you can buy ...
5
votes
4answers
10k 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 ...
5
votes
2answers
526 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 ...
5
votes
3answers
224 views

What makes materials hard and strong?

This is something I have wondered for a long time. Why are some materials like steel, diamond, and even light materials like graphene stronger than others? Is it due to the strength of the ...