Wikipedia:Reference desk/Archives/Science/2011 June 7

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June 7

Bowel and bladder control with ALS

Can people with ALS usually detect a #1 or #2 coming on and, if so, do anything to hold it in? 76.27.175.80 (talk) 00:22, 7 June 2011 (UTC)

Did you read ALS? if you look at the end of the 'disease progression' section your question is answered, to some extent. Richard Avery (talk) 07:10, 7 June 2011 (UTC)

The original question was as follows:

Can people like name redacted usually detect a #1 or #2 coming on and, if so, do anything to hold it in?

I re-worded the question to the version you see above, out of respect for the person named. Dolphin (t) 12:59, 7 June 2011 (UTC)

Mechanism of rotating gas cloud round gravity center

question :how dos any interstellar gas cloud rotate round gravity field ?(replay by intering all dynamic and termodynamic and statistical physics factors)--[[

Special:Contributions/78.38.28.3|78.38.28.3]] (talk) 03:00, 7 June 2011 (UTC)—Preceding unsigned comment added by 78.38.28.3 (talk) 03:00, 7 June 2011

Why don't you create an account? Your questions often look like homework but for those who know you it is clear that they are not, and that you ask out of genuine interest. It would also make it easier to put some advice or help on your discussion page. And, when you sign your posts with ~~~~ the user name you had chosen would automatically appear and you don't have to do all this signing by hand each time. 93.132.188.46 (talk) 10:50, 7 June 2011 (UTC)

And it would not be as easy for others to put misuse to your questions, pretending it came from you. 93.132.188.46 (talk) 10:53, 7 June 2011 (UTC)

I have to apologize for my silly proposal. I thought for myself: why not create an account for myself? But I failed for every try because all user names I could think of are already in use or rejected because they are too similar to some already existing ones. 93.132.188.46 (talk) 20:22, 7 June 2011 (UTC)

many thanks of your guid I have account and this is my signature(I am online now)--Akbarmohammadzade (talk) 04:53, 8 June 2011 (UTC) (talk) 04:47, 8 June 2011 (UTC)

To get to the actual Q, the cloud likely has a tiny rotation inherited from larger galactic rotation, which in turn comes from galactic cluster eddies, ultimately going back to the Big Bang (although what caused the initial rotation right after the Big Bang is a mystery). As gravity pulls the gas in closer, it spins faster, due to the conservation of angular momentum. StuRat (talk) 20:42, 7 June 2011 (UTC)

I want to know can any gas cloud or nebula be able to have momentum of inerthia , and center of mass?--Akbarmohammadzade (talk) 04:56, 8 June 2011 (UTC)

Yes, a cloud of gas has both. StuRat (talk) 08:09, 8 June 2011 (UTC)

You may want to read star formation, protostar and molecular cloud. ~AH1 ^(discuss!) 16:35, 11 June 2011 (UTC)

grouping and cross-matching in blood bank

can plasma be used (instead of serum) for blood grouping and cross-matching in blood bank? — Preceding unsigned comment added by Goldenvikie (talk • contribs) 17:07, 7 June 2011 (UTC)

Yes. Blood anticoagulated with EDTA is often used. Details here. --NorwegianBlue ^talk 20:55, 7 June 2011 (UTC)

How healthful is this bread?

I want to buy low-sodium, low-sugar 100% whole wheat bread, but it doesn't seem to exist. For some reason this bread [1] is not labeled as 100% whole wheat. What's your verdict? (The link includes a list of ingredients as well as the Nutrition Facts. 66.108.223.179 (talk) 19:14, 7 June 2011 (UTC)

I'm surprised it can be sodium free, since I thought yeast needed some sodium to grow. That bread looks to be healthy, though. StuRat (talk) 20:34, 7 June 2011 (UTC)

Not at all: you can make bread without salt very easily: it rises quicker, but tastes blander. Less of a problem if you spread it with salted butter ;) The yeast don't need the salt: the salt actually slows the rising down, which is handy if the weather is warm, you don't have a cool enough spot, and you want a slow rise for taste or convenience's sake. You can only take that so far before the bread is inedible, which generally hits well before you risk killing the yeast completely. 86.163.0.72 (talk) 20:46, 7 June 2011 (UTC)

You all are talking about different things. The OP is asking about low-sodium, StuRat reads this as "sodium free" and 86.~ talks about salt, and it reads as if he is talking about additional table salt (NaCl) that was not already present in the wheat. 93.132.188.46 (talk) 21:25, 7 June 2011 (UTC)

No, I think StuRat is refering to the bread in the link which is listed as sodium free. Richard Avery (talk) 22:18, 7 June 2011 (UTC)

How would it be possible to make bread literally sodium free? Not adding salt and using distilled water would sure be necessary but still there would be the sodium from the wheat. Plants, like all living things (live as we known it), contain essential parts of sodium. 93.132.188.46 (talk) 22:31, 7 June 2011 (UTC)

Yes, I refer to the 0 mg of sodium listed under the "Nutrition" tab on the link. Perhaps it's a case of "rounding down", and it really has a small amount of sodium. I still think that yeast must require some sodium to grow, but perhaps the small amount already present in the wheat and water is sufficient, with no need for added sodium. StuRat (talk) 08:02, 8 June 2011 (UTC)

Or perhaps they used KCl instead of NaCl to salt the bread? I think it's rather unlikely, but... 67.169.177.176 (talk) 00:03, 11 June 2011 (UTC)

This bread is healthful and widely distributed. Their "Yoga Bread" is very good but so are their other breads. The company is called "The Baker". They make granola which isn't bad either, though I prefer udi's granola—also widely distributed. Bus stop (talk) 23:40, 7 June 2011 (UTC)

Physics Is Phun!

A curious thing happened today. I got up from my seat on the bus before it stopped moving and as the velocity decreased exponentially I felt that I were going to fall forward. I compensated by walking faster. Now my question is, was I really walking faster, or was it an illusion? What are the pertinent functions and how can I notate this action? Schyler (one language) 23:27, 7 June 2011 (UTC)

A very qualitative discussion: Let's imagine the bus was going a constant speed, say, 25 mph. While you're sitting on the bus, or even walking around on it, you won't feel like you're moving at all — basic Galilean invariance. When the bus starts to slow down, your body is still going 25 mph, but you are slowing down along with the bus. (If the bus slows down immediately, you'll fly through the window at 25 mph, because you didn't adjust to the speed of the bus.) If you're up and walking around, you're going to be potentially not slowing down at the same rate as the bus itself, and thus feel an acceleration (a falling feeling). The illusion is that when you walk forward, you feel like you're speeding up. You're not — the bus is slowing down, but your relative speed vs. the relative speed of the bus is probably faster than the bus (e.g. the bus is going 23 mph, but you're still going 25 mph). --Mr.98 (talk) 02:10, 8 June 2011 (UTC)

Yes, you were walking faster. When you are seated, friction is equal and opposite to the stopping force causing the bus to lose forward momentum. Therefore, when you stand up during this time, friction is drastically decreased, meaning the stopping force is also decreased for you compared to the bus. This difference in stopping force inturn results in a decreased deceleration for you, i.e. you lose forward momentum at a slower rate than the bus. Plasmic Physics (talk) 02:26, 8 June 2011 (UTC)

Friction has nothing to do with this. It is a question of relative acceleration, as Mr.98 explains, though it is also a matter of how you 'perceive' this. If you are standing still, and start to tip forward, you put a foot in front of you. If you are walking, and start to tip forward, you compensate by walking faster. Try standing still in the bus as it brakes - you will step backwards to avoid falling. Essentially, you are trying to keep the vector of forces generated by your weight (vertically downwards) and the deceleration of the bus (horizontally forwards) acting through your feet - you have to move them forward of your centre of gravity to avoid falling over. AndyTheGrump (talk) 02:35, 8 June 2011 (UTC)

Sorry, not friction, but torque. Plasmic Physics (talk) 07:23, 8 June 2011 (UTC)

Let us assume that the you can be represented by a rigid lever arm, where your center of mass acts as the axis of rotation. Obviously, the force is applied to the level arm at the point of contact between you and the bus. If you are seated, your center of mass will be lower down than when standing, thus the lever arm will be shorter. The applied force is the same whether you are seated or standing. Because torque is a measure of the lever arm distance multiplied by the (orthogonally) applied force, you will experience a greater torque when standing. This is an over simplification, since in reallity a person has many active axes of rotation i.e. skeletal joints, and is not rigid. The effect of the greater torque on a standing person means that they will be rotated around their center of mass, resulting in gravitational torque. Gravitational torque causes you to fall forward, this is a result of the first toque produced by the stopping force. You do not fall over when seated, because you are ellastic enough to absorb the lesser torque. Plasmic Physics (talk) 13:55, 8 June 2011 (UTC)

I should qualify my answer just to note that if you were walking forward at any particular speed, you might in fact be speeding up slightly, but the forces you feel are not due to you speeding up so much as the bus slowing down, and you not slowing down with it. (The reason your walking forward will not matter much is because the relative speeds of the bus are so much faster than your relative speed of walking — you're already going 25 mph, and at most your very brisk walking is going to be another 1 mph or so.) --Mr.98 (talk) 13:49, 8 June 2011 (UTC)

Brisk walking is 3-5 mph. Googlemeister (talk) 18:28, 8 June 2011 (UTC)