Science Quiz

[The Last Conformist]

From long thin charged object, the electric potential falls as 1/r with increasing distance r from the axis. From a charged point, the potential falls as 1/r^2. The end of a long thin charged object approximates a point when seen from the direction opposite to the rest of the object.

Since the electric field is proportional to the gradient of the potential, the field is stronger near the sharp point where the potential falls quicker with increasing distance from the object.

 

[betazed]

Correct.

 

[The Last Conformist]

I was sure you were gonna ask why the potentials fall like that ...

For an object on the earth, the gravitational pull of the Sun is stronger than that of the moon. Yet lunar tides are higher than solar ones. Why?

 

[betazed]

Originally posted by The Last Conformist
I was sure you were gonna ask why the potentials fall like that ...

If I was doing a physics interview I would have asked that. But I guess people reading this thread (and you) would be irritated if I keep asking the why's of every answer that you throw at me?

But I wouldn't mind hearing why the potentials behave like that? Or for that matter why EM follows a 1/r^2 law and why the field from a flat surface follow a 1/r law.

 

[The Last Conformist]

The field from a flat surface fall as 1/r because the potential goes as ln r .

 

[betazed]

Originally posted by The Last Conformist
For an object on the earth, the gravitational pull of the Sun is stronger than that of the moon. Yet lunar tides are higher than solar ones. Why?

Tides happen not because of gravitational force but because of gravitational force differentials. The Sun being farther away this differential is small and the moon being much closer this differential is large. Hence lunar tides and higher than solar ones.

 

[The Last Conformist]

Yep. Your go:

 

[betazed]

Originally posted by The Last Conformist
The field from a flat surface fall as 1/r because the potential goes as ln r .

Well, we could go a little more than that.

But why the ln r potential. Because you integrate oven a infinite flat surface where each point is providing a 1/r potential. But why 1/r potential? because we have a 1/r^2 force law. But then why 1/r^2 force law. Because it is gauge force, and it is propagated by photons which are massless particles. So why massless photons? Because of Lorentz invariance. So why should there be a Lorenz invariance?

We do not know yet. (Or at least I do not know yet )

I will let someone else ask the next question. We do not want to monopolize this thread.

 

[Deep_Thought76]

Ok, since betazed opened it up and no one else has come forward, I'm going to pose a question. We've had a bunch of tough physics ones, so now it's time for some biology. This is a common example in many textbooks, so it should be pretty easy.

In the early 1960s, the drug Thalidomide was used in Europe as a mild sedative, to combat morning sickness during pregnancy. The active component of the drug was safe and worked as intended, however, the drug as a whole was found to cause severe birth defects. This was due to another component, present in equal amounts with the active one, which was harmful when taken during the first trimester. The thing is, this other component had the same formula (ie. the same numbers and types of atoms composing it) C13N2O4H10, and the same molecular structure (ie. those atoms were connected to each other in the same sequence). It was (for the most part) physically and chemically indistinguishable from the active component. Furthermore, the makers of the drug knew the harmful component was present, although they didn't think it would have any effect.
So: How could this have happened? What was the difference between the 2 molecules? Why were they present in equal amt.s? And, why did the drug's makers think that including both wouldn't cause any problems?

 

[slothman]

I would guess from your information they are sterio isomers. The bonds are the same in 2D but different in 3D. Even a trans/cis difference would probably not create equal amounts.

 

[Guildenstern]

The difference is in chirality. There are right- and left-handed versions of the molecules (mirror images).

I don't have any questions; if that it the answer you're looking for, someone else can put up a question.

 

[Perfection]

Chirality is the same thing as stereoisomerism.

 

[slothman]

Yeah that's the word. The difference between L-CHFICl and D-CHFICl.
EDIT: I changed R to D because of the weird systems they use. [L]evulose and [D]extrose or [R]ight and inister. Why not [L]eft and [R]ight?

 

[Guildenstern]

Originally posted by Perfection
Chirality is the same thing as stereoisomerism.

Oh. Well then. Organic chemistry isn't really my thing.

 

[Perfection]

Originally posted by Guildenstern
Oh. Well then. Organic chemistry isn't really my thing.

Hey, you know more than 99% of the population!

 

[Deep_Thought76]

Wow, 3 correct posts in an hour. I guess Slothman answered first, so he can ask the next one.

More info: Yes, it's everyone's favorite subject, ochem! Specifically, these compunds have a 'chiral center', making them mirror images at that point. Hold 1d4 up to a mirror and you'll see what I mean. When you're just making these things in the lab, it's random whether the product of the reaction will be one 'enantiomer' or the other. So, you'll get a 'racemic mixture', 50/50 of each. Living systems are almost always 'stereospecific' and 'stereoselective', meaning that they only produce and use one of the enantiomers of a molecule. (This is because the reactions are not done free-floating, but use enzymes talior-made for each step in the reaction.) So, most of the time, one half of a drug's mixture is active, the other half is simply inert. In this case, the other enantiomer was active, with awful results.
Another example of the importance of chirality is in flavors. Spearmint oil and carroway seed oil are actually enantiomers as well. A certain %age of the population, myself included, has a genetic defect that makes them unable to tell the difference between the 2 compounds. Ie. the receptors on their tongues aren't selective, and so the 2 flavors taste the same.
This has been More Than You Ever Wanted to Know About Stereochemistry™.

 

[slothman]

Ok what is the shape of the Moon's orbit around the Sun? Assuming a simple system with only the Earth, Moon, and Sun.

 

[greentea]

Do you need the name of that shape or an equation? If the latter, in what coordinates?

 

[zurichuk]

post deleted for fear of being made to look like an idiot thought it was the trick thread

 

[slothman]

Just the shape.