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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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 ...
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3answers
570 views

Can vinyl LPs store audio above 20kHz and can it be played back? [closed]

If, in the future, humans genetically engineered themselves to be able to hear frequencies significantly above 20kHz (say, up to 100kHz), would they find vinyl LPs a viable method of storing and ...
4
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2answers
346 views

Why magnetic monopole found in spin ice don't modify the Maxwell's Equations?

Magnetic monopole predicted by Dirac nearly a century ago was found in spin ice as quasi-particle(2). My question is Why magnetic monopole found in spin ice don't modify the Maxwell's Equations? (I ...
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4answers
6k 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 ...
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3answers
15k 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?
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3answers
337 views

How to block neutrons

What is a good way to block neutrons and what is the mechanism that allows this? It's my understanding that polyethylene is somewhat effective. Why?
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3answers
4k views

Space Elevator on Mars with Today's Technology Possible?

I know it's not possible with Earth today, but With today's level of material science technology, would it be possible to make cable strong and light enough to make a space elevator system connecting ...
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5answers
5k 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 ...
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1answer
156 views

Why do neutron stars have solid crusts?

A long time ago I read that neutron stars have a solid crusts that are several orders of magnitude harder/stronger than alloys here on the Earth. So how is this possible ? A neutron star has a ...
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1answer
135 views

Why can gold be drawn out finer than light?

The metal gold is extremely malleable. Gold is also ductile and one ounce can be drawn into 80 km (50 miles) of thin gold wire (5 microns diameter) to make electrical contacts and bonding wire. I ...
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2answers
190 views

Does the Night Mode of the screen display (LCD) save more energy? [closed]

In some cases, we can enable the Night Mode (reversing the bright and dark color of the display; such as White Text, Black Background) for the screen display. LCD(Liquid-crystal display) seems to be ...
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2answers
518 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 ...
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1answer
646 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 ...
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2answers
985 views

Mnemonics to remember various properties of materials

I'm trying to figure out how to remember that hardness: how resistant it is to deformation toughness: how resistant it is to brittle failures stress: force on a surface area strength: ability to ...
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1answer
138 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?
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1answer
155 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 ...
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1answer
72 views

Breaking strength of wet paper/cloth

In the Hollywood movie, Shanghai Knights (pardon me for the non scientific citation), Jackie Chan states that 'wet cloth' does not break easily. How true a fact is this ? We know from common ...
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1answer
46 views

Why does melted agarose in solution appear fully transparent, but become opaque when polymerized?

Agarose gels (hydrogels) are commonly used in molecular biology for electrophoresis of DNA. When a solution of hot agarose is poured, the material is clear: When a gel forms, the material ...
4
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1answer
111 views

Why does the refractive index not mirror the Lorentzian peak shape of the absorption index?

In the characterization of materials, there are many methods used: One of them is infrared spectroscopy. In a lab we saw the indices of refraction and absorption of a certain (semiconductor) solid ...
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2answers
112 views

Could a long carbon nanotube be broken by hand?

Assuming we could get a single nanotube a metre long, would it be possible to break it by hand or would it slice through just about everything including flesh and bone? Could we even grip it, or would ...
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2answers
96 views

Why nano indentation is used to test bulk material?

I am curious why nano indentation is used? I can understand when material size goes to micros or below, conventional hardening methods can become difficult to use. However many papers say that ...
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1answer
363 views

If atoms have specific energy levels, why do opaque solids absorb all visible light, not just some? [duplicate]

Here's my question: if atoms have well defined energy levels and those differences correspond to the frequencies of light that can be absorbed, how is it that opaque objects absorb all or most visible ...
4
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1answer
220 views

Wall stress of a hexagonal pressure vessel

Problem: I want to calculate the stress in the walls of a hexagonal pressure vessel but I can't manage to get coherent results. For long vessels, cylinders are supposed to have the lowest hoop stress ...
4
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2answers
336 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?
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2answers
1k 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
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1answer
61 views

Is diamagnetism a static or dynamic effect?

When we put a diamagnetic material in the presence of an external magnetic field $\vec B_0$, the magnetic field inside the material decreases to $$\vec B=(1+\chi_m)\vec B_0,$$ where the magnetic ...
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2answers
202 views

First-principles derivation of cutting force

I know that the amount of force required to separate a material from itself is linked to the surface energy of that material. However, looking at just the surface energy laughably underestimates the ...
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1answer
659 views

Why is powdered sugar less dense than granulated sugar?

The density of powdered sugar is about 20% lower than that of granulated sugar. There is small composition difference between the two - about 3% cornstarch and 0.5% water in powdered sugar, but that's ...
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2answers
61 views

What keeps objects made of the same plastic apart?

I have two objects here which are made of the same plastic. When I hold them together, they remain separate objects: I can pull them apart with no resistance. How does each atom/molecule “know” which ...
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2answers
565 views

Why are there direct bandgaps?

This Question has been bugging me for sometime. Some semiconductors have direct bandgaps and indirect bandgaps. So what causes a direct bandgap to occur? The physics behind ,why there are direct ...
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3answers
304 views

What is the difference between material fatigue test with 1 sec cycle and 1 hour cycle?

Assume I have two pieces of metal. I want to test the material fatigue (e.g. how many cycles can the material stand before it will break). Onto one of them I apply a tension force every second. Onto ...
4
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1answer
263 views

(Botanical) branch bending under gravity

I'm a PhD student in maths, and attended my last physics class some 15 years ago, so you can imagine my competences in the field. My supervisor (also not a mechanist) cant tell me how to proceed ...
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2answers
300 views

Can a minimum ultimate tensile strength (UTS) for an asteroid be established based on its diameter and rotation?

I found it fascinating that many asteroids rotate with a period of just seconds. For this fast of a rotation on this size of object, I thought that would actually cause significant acceleration on the ...
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2answers
279 views

Is it possible for an object to have low specific heat capacity and low thermal conductivity?

As I see, there are many examples of object with low specific heat capacity and high thermal conductivity and vice versa. Since they are different properties of matter and their definitions are not ...
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1answer
75 views

How can one reasonably theoretically model polycrystalline materials?

Many techniques are taught in advanced solid state courses but they are almost all derived for perfectly crystalline materials. For example, band structure really only appears theoretically when you ...
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0answers
111 views

What physical properties of silver would contribute to the sound of a musical instrument? [closed]

A question was recently asked on Musical Practice & Performance, asking what physical properties of silver would contribute to the sound of percussion instruments. It is likely to be off-topic ...
3
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5answers
55k views

Yield Strength versus Ultimate Strength

What is the qualitative difference between these two: As seen on the table Typical yield and ultimate strengths. I am trying to resolve the meaning of the phrase "contact yield stress" from C. ...
3
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2answers
381 views

Does metal under low tension ever actually bend?

Let's assume something like a pair of tweezers, since that's strangely what led to this mental exercise. Does the metal ever actually permanently transform its shape? Stainless steel is fairly ...
3
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3answers
166 views

How does radiation degrade mechanical parts and electronic devices?

I'm running out of places to look (lots of Googling, SE, [articles and books are too specific and never give a good overview]), and yet I am still unsure about how exactly radiation can degrade ...
3
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2answers
392 views

What makes a material a good lens for CO2 lasers?

I read on Wikipedia that zinc selenide and germanium make good lenses for $\mathrm{CO}_2$ lasers. My question is, Why?
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2answers
180 views

Can a liquid shrink as something is dissolved into it?

Not much more to add. By shrink, I mean become more dense at the same pressure and temperature. And I don't mean vol(A+B) < vol(A) + vol(B). I'm sure this is possible. Is it possible to ...
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1answer
980 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?
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3answers
252 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
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
4answers
330 views

Surface area of glass (or general material) and strength

How does the surface area of a piece of glass (or any general material; sapphire isn't technically glass) correlate with strength? Strength as in resistance to pressure concentrated at a small point? ...
3
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2answers
147 views

Can Aluminium be softened

I have an aluminium baking plate that I did put in a very hot oven and now it is soft, so I can bend it or almost roll it up. Why?
3
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2answers
2k 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
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1answer
62 views

Sonic boom breaking glass

It's a well known fact that a sonic boom from something such as concord can shatter glass. I'm interested to know why a human is seemingly fine in the presence of the shockwave and yet the glass is ...
3
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1answer
34 views

Effectiveness of phase-change materials vs water for heat storage?

I'm trying to understand the benefit of specialized phase-change materials vs. water for absorbing heat in a home during the day. It's my understanding that selecting phase-change materials whose ...
3
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2answers
225 views

With a machete, why is a diagonal cut more effective than a right angle one?

When cutting back some thick growth in the garden a question that always nagged me. Why is cutting diagonally seemingly more effective than cutting at right angles? Part of the answer is obviously to ...