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Page 44 of 160 (1595 Questions and Answers)

431. Why can't I record songs directly onto CD's, like I can onto a tape?
To record CD's, you need a much more powerful laser and a blank recordable CD. Both of these items cost lots of money. Reading a CD does not alter the CD but writing it does. You need more laser power and a special CD disk. If you tried to record a normal CD, you would not be able to restructure its aluminum layer. You would not "erase" the old material on it and would not "write" new material onto it.

432. Why do CD's skip?
CD players must position their optical system very precisely, relative to the spinning disk itself. It uses very sophisticated electromechanical devices to keep it in place. But if you jar a player violently enough, it will lose its position and the audio may suffer. Most modern CD players save a short amount of information so that they are reading ahead of where they are playing. Even if they lose the track for a few hundredths of a second, they have enough music saved up that they can keep playing continuously. But if the upset is severe enough, they will run out of saved music and will go silent for a moment or two.

433. Why do some CD players sound better than others even if the CD is seriously scratched on the bottom half?
At this point, there should be very little difference between CD players that are playing perfect CD's. They all create almost distortionless reproductions of the original sound. However, different players use different tracking techniques and optical systems and thus have different abilities to recover from imperfections in the CD.

434. Why do you need to separate the different polarizations of light?
Any light wave can be described in terms of horizontally and/or vertically polarized light. For most things, these two polarizations are unimportant. But when light reflects from surfaces or passes through certain materials, these polarizations become important. The charges in surfaces and materials do not always respond equally to the two polarizations of light. The two polarizations may even travel through very different paths (e.g. in the polarization beam splitter).

435. Will light going in two directions in the same space create destructive interference?
In general, the answer is no—there won't be large regions of space in which the two light waves cancel one another. That's because, while the electric fields from the two waves do add to one another at each moment, those fields go in and out of phase with one another very rapidly as the waves pass and the end result is that they do not interfere with one another over broad expanses. However, there can be points or surfaces in space at which the electric fields from the waves at least partially cancel for extended periods of time and at which there is destructive interference. These points and surfaces are often observed in experiments with single frequency laser beams.

436. How do steak knives differ in structure from the "super" cut-through-anything non-damageable knives?
A good knife is distinguished both by its cutting edge and the backbone that supports that edge. The ideal knife has a very hard cutting edge (one that never undergoes plastic deformation and thus never becomes dull) and a very tough backbone (one that can absorb an enormous amount of energy before breaking). The backbone can experience plastic deformation when necessary, in order to absorb energy. Cheap steak knives are made of only one steel: a moderately hard and moderately tough material. They gradually dull because of plastic deformation in their edges but they never break because their backbone is flexible. A great knife is made of several steels, which can be formed by proper heat treatment of a single piece of metal: a very hard edge and a very tough backbone. It never gets dull because its cutting edge never yields and it never breaks because it bends before breaking.

437. How is the strength of a clipping device such as Caribeener, hook, or chain link calculated? I think it is measured in kilo-newtons. What elements are taken into consideration when that strength is measured?
One of the most critical measures of a clip-ping device is the maximum tension that it can tolerate without failing. I would expect a tester to measure that failure tension by putting the clipping device in a simulated working environment and exposing it to greater and greater tension until it fails. For example, a chain link would be put between two sturdy hooks and then the hooks would be pulled apart until the chain link broke or deformed permanently. Since tension is a force, it's natural to measure it in newtons or kilo-newtons (1000 newtons). (There are 4.4482 newtons in 1 pound of force.) But what constitutes failure is complicated since anything that is exposed to tension deforms somewhat. However, if the tension is less than a certain threshold, the deformation will be purely elastic—meaning that the device will return to its original shape once the tension is released. But if the tension exceeds that threshold, the deformation will be plastic—meaning that it will be permanent and the device will not return to its original shape once the tension is released. I would expect the rated strength of a clipping device to be a reasonable fraction (probably about 50%) of the tension required to cause plastic de-formation of that device.

438. Is it true that striking two hammers together will release little splinters? If so, why?
The head of a hammer is made of very tough steel. Depending on the type of hammer, that head may even hardened tool steel. In that case, the head will not yield, except to the most incredible forces. It will instead deform elastically and then return to its original shape. However, if you smack two hardened hammerheads against one another, the forces that they exert on one another may become so great that the heads will shatter. The symptom will probably not be the release of a few tiny splinters but rather large chunks of hard steel flying off in all directions.

439. What makes stainless steel stainless?
Stainless steel resists corrosion because one of the metals (iron, nickel, and chromium) or one of their oxides is bound to be stable in almost any chemical environment. Corrosion stops at the grain boundaries around the stable materials so that they form a protective layer above the other materials beneath them. — Thanks to David Ingham for this answer

440. Why is silver used so often for tableware?
Silver is used in tableware because of its whitish luster and preciousness. It is not really the most practical metal for cutlery. It tarnishes slowly by reacting with sulfur pollutants, which are present in the air in trace amounts. Pure silver is also very soft because it allows slippage to occur easily. To harden tableware, silver is alloyed with about 5% copper. The resulting material is much harder than either of the pure metals. Jewelry silver has even more copper; up to about 20%.
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