Easy Questions?

[The Meromorph]

Why do tennis players bounce the ball up and down immediately prior to serving? (I find it irritating, as I do the grunting too).

At the level the pro's play at, a new ball 'goes off' fairly rapidly (after a couple of dozen hits). The 'ball boys' are issued a set of two dozen balls at the start of a match, and they are cycled randomly in use. Some of them naturally get used more than others. The players are testing each ball before they serve to see if it has 'gone off' (It won't bounce as high or as fast). If one is not to their satisfaction they will throw it to, or sometimes at, a 'ball boy' who is supposed to remove it from play. When there are insufficient balls to keep an adequate stock available, the umpire will call for 'new balls please!', and all the balls in play are retired and a full new set issued.

[Aggie]

What are the implications of an electromagnetic wave with a wavelength approaching zero and a frequency approaching infinity?  Head for the far end of gamma and keep going....  does it change from a wave into something else?   Does it become mass?

I'm curious about the other side of the coin (near-infinite wavelengths), but that seems easier to get a handle on as they'd be low energy to the point of non-energy.

[Swatopluk]

I guess it would condense as matter but the wavelength would have to be considerably shorter than even that of hard gamma-rays.
It all of course requires that the amplitude does not go to zero too.

[Aggie]

Yes, assume amplitude is kept nonzero and constant.

[Swatopluk]

White dwarf matter shows up in physics text and occasionally comic books. It is famously very dense with about 10 tons per cubic centimetre. It is in a pysical state known as degenerate but not fully collapsed (as in neutron stars).
My question: if a piece of a white dwarf would be removed and brought elsewhere, would it stay in this superdense state or simply revert to normal because the gravity causing the degeneration is absent?

[Sibling Zono (anon1mat0)]

I suspect that to properly answer this definitively not easy question, a deep knowledge of theoretical quantum mechanics and astrophysics is required. The intuitive answer is that it would likely revert to normal matter in a violent fashion, but considering that quantum mechanics are all but intuitive I cannot say that that would be the actual behavior.

[Sibling DavidH]

I know less about Quantum Physics than most people, but ignorance has never inhibited me from saying my pennyworth: 

Doesn't it depend on the mass and shape of the detached lump?  A big enough lump would surely maintain its state, a small one would not hang together.

[Aggie]

Do hot beverages have an effective caloric value based on the amount they heat up the body (which displaces the need to burn food for heat)?

Back-of-the-napkin calculation would suggest that assuming an average consumption temperature of 60 C, this would represent about 22.5 kCal/L.  Less than having a spoon of sugar in each cup.


Related question, in that case: Do hot beverages actually have the potential to warm you up?  I've felt like I was overheating when eating hot soup or drinking hot tea, but since the amount of actual warming that say, 500 g of 60 C water could perform on a 75 kg body is negligible (roughly 0.15 of a degree), the usefulness in warming up a hypothermic person seems pretty limited. 

If one is at a normal body temperature and normal room temperature, the production of sweat might a) take calories to effect and b) provide evaporative cooling that requires additional calories of food-energy consumption to compensate for.

I don't propose a significant effect, but overall, does drinking plain hot water represent a gain or loss of calories?

[Swatopluk]

That looks related to the myth of negative calories, like eating frozen food or stuff that uses up more energy in chewing than it yields in calories. One factor notoriously ignored there is that heat exchange takes place not just between the food and the body but also between both and the outer environment.
As for warm liquids for treatment of hypotheremia, I think the main effect is less in the amount of calories transferred but in the speed it takes place. The heat has to be transported where it is needed quickly without the body having to do much muscular activity. The nutritional calories have to be turned by the body into fuel for muscles and the muscles have to turn them into heat. A hot liquid will transfer its heat to the body instantly.

[Sibling Zono (anon1mat0)]

I suspect that external temperature has a good deal to do with it, that is, if you are in a hot weather the extra heat will force your body to burn energy to cool you, while in a cold weather it will reduce the amount of energy you use to keep your temperature. My hypothesis is that while the actual heat of the hot beverage isn't that great while measured in kCal, it is warming directly your internal organs (which are the ones in critical need of heat) and the energy expenditure of the body to heat it in the same proportion is significantly higher due to inefficiencies while converting fat to heat.

[Swatopluk]

But the inefficency is already in there through the calories given as nutritional value not enthalpy of combustion.

[Griffin NoName]

I just watched a really bad explanation of bio-synthesis on TV.

Essentially it went like this:

Making Cynthia:

Clive wotsit took a cell, (cell A) extracted it's DNA and put it (the DNA code) into his computer. Then he took another cell (cell B), extracted it's DNA and threw it away. Then he synthesised the DNA code in the computer (cut to picture of a printer printing out the letters of the DNA code - voice over saying just like this) and inserted it into cell B (picture of piece of paper with letters of the DNA code, shown hovering over cell B- so now cell B has cell A's DNA and is therefore a synthetic life form - Cynthia.

What the hell does "Then he synthesised the DNA code in the computer " actually mean? What did the computer DO? What actually came out of the computer? Why is a computer needed at all.?

It didn't help that he used drops of wax to simulate the cells.

[Bob in a quantum-state-of-faith]

I just watched a really bad explanation of bio-synthesis on TV.

Essentially it went like this:

Making Cynthia:

Clive wotsit took a cell, (cell A) extracted it's DNA and put it (the DNA code) into his computer. Then he took another cell (cell B), extracted it's DNA and threw it away. Then he synthesised the DNA code in the computer (cut to picture of a printer printing out the letters of the DNA code - voice over saying just like this) and inserted it into cell B (picture of piece of paper with letters of the DNA code, shown hovering over cell B- so now cell B has cell A's DNA and is therefore a synthetic life form - Cynthia.

What the hell does "Then he synthesised the DNA code in the computer " actually mean? What did the computer DO? What actually came out of the computer? Why is a computer needed at all.?

It didn't help that he used drops of wax to simulate the cells.

Actually?  The physical DNA that was inserted was made up of it's base components, and not other DNA molecules.

They used the sequenced DNA of cell A as a road-map, but not exclusively-- they added in some other bits as proof-of-concept, chiefly one that makes the new cell glow under certain light.

But essentially, the copied the majority of the DNA's 'alphabet' into a computer, via gene sequencing methods.

And they took the code--after tweaking it as above-- and used that artificial sequence to re-create, out of raw chemicals, the new DNA.

And finally, using viral methods, the re-inserted the artificially-created DNA into the host cell-- one that, without any DNA, was effectively dead-- it could not reproduce, nor could it repair itself, nor could it metabolize nutrients.

Once the artificial DNA was inserted, the cell started to metabolize nutrients, and soon enough, reproduced-- the daughter cells faithfully glowing just as the parent cell did.  And so on-- I don't know how many generations they let it go, before killing the whole batch.  Quite a few, I'd imagine.

But the whole point, was at one step, the entire DNA only existed as computer code--

-- in a way, kinda-sorta, they "beamed" the DNA from one cell to the other, via computer code.

There really would have been no reason why they couldn't have telephoned that code around the world first-- it had been reduced to digital information-- one's and zero's in a computer's memory banks.

Kinda amazing, really.

[pieces o nine]

...and inserted it into cell B (picture of piece of paper with letters of the DNA code, shown hovering over cell B...

Wow!  That sounds eerily similar to the way the BVM conceived the Baby Jesus, as explained rather early in my religious indoctrination education, what with an asexual [object] hovering magically above a sexually reproducing [object] without any physical contact, and all...

[Griffin NoName]

But the whole point, was at one step, the entire DNA only existed as computer code--

Sorry, but I don't find that amazing at all. I can't see anything all that clever, once computers have been invented, and once DNA can be reduced to a sequence of letters, about the use of a computer to produce an adulterated sequence (ok, it is a bit clever to define the DNA sequence specifically needed to cause glow, and program the computer to combine etc but still, the basics are all there as far as the computer aspect was concerned). For me that was not the whole point. The whole point seems to me the method of re-introducing the newly sequenced code into the cell from which its own DNA has been removed. To demonstrate this by holding up a piece of paper with a load of letters on it, printed out by a computer, explains precisely nothing. The point of the program was to explain it, and it didn't.