# Tag Info

2

I tend to agree with Sanya in that I am not sure about the universality of this. There might of course be instances where this is the case. A pure metal has a periodic lattice of ions. There is then a conduction band of electrons that fills the space between the ions. These electrons have wave vectors in the reciprocal space. In space the occurrence of ...

1

First of all, I want to see an (experimental) proof that any metal has a higher resistance than any alloy (at any pressure, temperature and volume). What I presume your teacher might have wanted to hear is something along the following lines: a perfect, perfectly static crystal would be, if I remember correctly, perfectly transparent to an electron, so there ...

0

You may find this link interesting. 19th century research indicates (for iron/steel armor and iron balls) a formula along the lines of $$T = .00005D\sqrt{\frac{W\times V^2}{D^3}}$$ where T is armor thickness, V is velocity, W is weight and D is diameter. This assumes pretty much perpendicular impact on the armor face.

1

Your question is really broad. As correctly pointed out by @John Rennie there can be so many signals that can pass from the solids. It must be noted that even if the signal can pass through solid it will experience certain losses. Mechanical waves such as sound took advantage of elasticity of the material. The sound oscillations are transferred through ...

-2

Most objects are porous and allow the elector-magnetic signal through. Little electrons can pass through what appears to be solid material like photons through glass. Some are still trapped in the atoms. Denser metals like lead do not have enough space between the atoms to allow the electromagnetic waves through. Certain wavelengths can pass through certain ...

1

When a substance undergoes a phase change such as melting, its chemical makeup remains the same. However, when heat is added to wood, the wood oxidizes before it would be able to melt. Wood contains long-chain organic molecules that decompose into products such as charcoal, water, methanol, and carbon dioxide upon heating. The physical structure of wood is ...

1

The basic problem is that headphones are heavy and asymmetric, whereas there's nothing attached to the shoelace. What this means is that the headphone - cord system can get stuck in stationary, locally but not globally minimum energy configurations: the twisting of a cord raises the energy of the cord, but the torsion resulting from the twist is not enough ...

10

Most ceramics are ionic compounds, in which electrons are immobile. This is different to metal, in which the atoms are in a "sea of electrons" that are free to move. Note that ceramics have some kind of conductivity, it's just extremely low. The conductivity of copper, for example, is ~6×107 S/m. Most ceramics have conductivities in the range of 10-3 S/m to ...

11

Solids can be classified according to their band gaps. The band gap determines how much energy you need to supply in order to free or promote an electron from the valence band to the conduction band. Once in the conduction band the electron can move nearly freely and conduct electricity. A solid with a large band gap (> 2.5 eV) is considered to be a good ...

14

For electricity to flow, electrons need to be moving. So in a conductor, there need to be free or loose electrons so they can carry the flow of electricity. Most metals fulfill this requirement, which is why most metals are conductors. Insulators, therefore, must have their electrons bound tightly, so they cannot carry the flow of electricity. The type of ...

2

A plastic flow is a deformation of a material that remains rigid under stresses of less than a certain intensity but that behaves under severer stresses approximately as a Newtonian fluid. In other words, let's say you have a sheet of plastic (though plastic flow can happen to not-plastic items) and you put it across two blocks and put weight on it, ...

1

Materials that seem homogeneous often have internal strains, or voids, or even inclusions. Under stress, rather than uniform deformation (bending), those flaws may undergo brittle fracture, or stretch excessively, or become chemically active. A cosmic ray can create internal damage, a particle decay track. So, after some kinds of handling (bending, ...

0

Strength and Toughness Image source: Materials Group - University of Cambridge We need the separate words "strength" and "toughness" because sometimes materials with high toughness and high strength are very different, like rubber and ceramic. Let's say you are designing a chair so that can support a person of a certain weight. Why not build it out ...

1

As CuriousOne said, the forces may be said to "exactly cancel" and be neglected only if they act on the same part of the body, i.e. if both of them act on the center of mass (or on the whole object "uniformly"). That's not the case when the object is deformed. The simplest example is to imagine that the object is a pair of cubes connected with a spring. ...

4

The effect you noticed is a function of strength and size. When you have a large window, and a sonic boom comes along, a relatively small pressure difference can set up very large tensile forces in the surface of the glass (especially if the shock wave cannot easily "go around the back" of the glass). When there is a bending stress, all you need is a small ...

4

Assuming the deck doesn't bulge to much at at the sides (as the video suggests), the press exerts work $W$ on the deck acc.: $$W=\int_0^yFdy$$ With $F$ the force exerted by the press and $y$ the displacement. This work is converted to potential energy and stored in the deck. As suggested in the answer to this question, the high pressure is likely to ...

1

Your equation for gas permeation mostly applies to hydrogen, which will dissociate into hydrogen atoms before entering the material. For nitrogen (major component of air), the equation has no square roots. Nitrogen permeation is extremely slow; if the box is welded shut and there are no cracks, then this process will be negligible, even over a 10-year period....

Top 50 recent answers are included