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53

Hard though it is to believe, pH does have an effect on sound absorption in water. There are some reactions that are affected by pressure, that is pressure changes their equilibrium. One example is the equilibrium between boric acid and the borate ion: $$ B(OH)_4\,^- + H^+ \rightarrow B(OH)_3 + H_2O $$ Increasing pressure pushes the reaction over to the ...


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 ...


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 ...


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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 ...


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 ...


3

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 ...


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, ...


2

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 ...


2

First, I'd like to point out that at this point the Dyson Sphere is purely theoretical in nature. Second, currently all plans to build a Dyson Sphere are, in the words of this website, far beyond humanity's engineering capacity. Portions of the technology involved in the Dyson Sphere have been developed, however, such as solar sails (a method of ...


2

Abrasive is intended to increase friction. You want your brake pads to have (and retain) a certain shape, so you use some structure material that resists well to changes in temperature. Not sure what performance material is supposed to be. In order to limit the costs, in places where no structural integrity is threatened, and no friction exists, you can use ...


1

The author should have been more specific on the matter or at least provide a reference. The speed of sound in water depends on the bulk modulus and density of the water, so in the open oceans the factors that most affect the speed of sound are salinity, depth (pressure) and temperature. I was an ocean engineering major and have taken courses in physical and ...


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 ...


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 ...


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, ...


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. ...



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