Science questions not worth a thread I: I'm a moron!

Status
Not open for further replies.
Natural log(x) is the area under the curve 1/t from t = 1 to t = x. It's the "missing" function when integrating powers of x. It also occurs naturally as the inverse of exp(x), which is the function which has the same value as its derivative at all points.
 
Blue Emu said:
... but the six pure numbers are derived in entirely different ways, from different groupings of fundamental constants! Given a "field" or span of eighty-odd orders of magnitude, what are the odds that the six numbers would lock into such an exact pattern? Is something mysterious going on, "under the hood" of Physics? Or is it just an outrageous coincidence?

My question, then: has any work been done on this "problem" in the past thirty years or so... or is it not considered to be a valid field of research?
Click to expand...

I don't know how you arrive at six, or which six you mean, because as it turns out there are twenty-something independent parameters in our current model of physics.

But the question why the parameters have the value they have is a major problem in modern physics. So far, the standard model has been extremely successful in describing almost all measurements, but it depends on about 20 parameters, which is considered unsatisfactory for most physicists.

A lot of work has been done in the last 30 years to solve this problem by finding an underlying theory that would explain these parameters, but so far no approach has really been successful.
 
Is allicin a good conductor of electricity?

Is running water a better conductor of electricity than still water given a constant water temperature?
 
Gatsby said:
Is running water a better conductor of electricity than still water given a constant water temperature?
Click to expand...

No, I don't think so. Water conducts electricity via ions dissolved in the water. As water is usually neutral, it contains negative and positive ions so that the total charge is zero. Both types contribute to the conductivity. So any gain in conductivity by one type of ions downstream will be offset by a loss of conductivity by the other type upstream.
 
uppi said:
No, I don't think so. Water conducts electricity via ions dissolved in the water. As water is usually neutral, it contains negative and positive ions so that the total charge is zero. Both types contribute to the conductivity. So any gain in conductivity by one type of ions downstream will be offset by a loss of conductivity by the other type upstream.
Click to expand...

Actually, wouldn't running water be a worse conductor than still water?... because a Lorentz-Contraction-type formula would apply.

As a thought experiment, consider what would happen in the limit, when the water is flowing exactly as fast as the ions could migrate. The negative ions could reach the down-stream electrode in half the time... but the positive ions couldn't reach the up-stream electrode at all! No current would flow.

Re: the six dimensionless numbers mentioned above... I was following an old paper by John Archibald Wheeler, reprinted in "The Encyclopedia of Ignorance". He singles out those six dimensionless numbers for discussion. Martin John (Baron) Rees... the current Astronomer Royal... also came up with a table of exactly six dimensionless numbers, although I don't know whether they are the same six.
 
I would think water would have to be travelling really really fast for that to happen. While the individual ions will show a bias in movement along with the current, there's no reason they can only travel in that one direction.

You'd need to figure out how fast electricity travels through water and I couldn't find that figure on google with a rather lazy search... I imagine rather slowly compared to a copper wire(95-97% of C). But even at .001% of copper's conductivity, the charge would be moving through water at 3km/s which is more than enough to overcome any flow rate.
 
contre said:
But even at .001% of copper's conductivity, the charge would be moving through water at 3km/s which is more than enough to overcome any flow rate.
Click to expand...

It would overcome the flow rate, correct... but the two opposing tendencies would create an equilibrium that was slightly lower than the equilibrium in still water... no?

In the same sense that time runs slightly slower on the ground floor of a building than on the roof. Very, very slightly slower, but slower nonetheless.
 
Blue Emu said:
Actually, wouldn't running water be a worse conductor than still water?... because a Lorentz-Contraction-type formula would apply.
Click to expand...

If you apply the Lorentz-transformation here, you indeed transform the current, but you also transform the charge distribution and thus the voltage. As conductivity is current over voltage I am not sure in what way the conductivity would change.

But the discussion is mostly academic, as water moving at relativistic speeds would destroy anything in its path, so it would be hard to make a conductivity measurement, anyway.

As a thought experiment, consider what would happen in the limit, when the water is flowing exactly as fast as the ions could migrate. The negative ions could reach the down-stream electrode in half the time... but the positive ions couldn't reach the up-stream electrode at all! No current would flow.
Click to expand...

Actually, the negative ions would still provide a current. There is no need for the positive ions to reach the electrode (in a "normal" conductor it is also just the (negative) electrons providing the current). There would just be no contribution from the positive ions. If you accelerate the water even further, the positively charged ions would be moving backwards, so they would start to cancel out the contribution of the negative ions.

Re: the six dimensionless numbers mentioned above... I was following an old paper by John Archibald Wheeler, reprinted in "The Encyclopedia of Ignorance". He singles out those six dimensionless numbers for discussion. Martin John (Baron) Rees... the current Astronomer Royal... also came up with a table of exactly six dimensionless numbers, although I don't know whether they are the same six.
Click to expand...

They don't seem to be the same. And that is hardly surprising, as there are a lot of ways you can define such numbers.
 
I have an engineering question.

I'm reading about Diesel-Electric locomotives, and the article mentions that they were favored over purely petro-fired engines because only electric motors are capable of supplying full torque at 0 RPM. I do not understand this statement. Why are electric motors uniquely capable of this and why is this desirable in a train locomotive?
 
Cheezy the Wiz said:
I have an engineering question.

I'm reading about Diesel-Electric locomotives, and the article mentions that they were favored over purely petro-fired engines because only electric motors are capable of supplying full torque at 0 RPM. I do not understand this statement. Why are electric motors uniquely capable of this and why is this desirable in a train locomotive?
Click to expand...

http://en.wikipedia.org/wiki/Diesel-electric_transmission
It sounds to me that what the wikipedia article is saying is that a piston of a combustible engine that is attached to wheel axle (where the engined torque is applied) is stymied by the amount of expansion of the piston. With combustion as the source of the torque, the energy is supplied by a chemical reaction which is under physical constraints (V, T, P) and if say the wheel were stuck, the piston would be stuck so that the combustion chamber was at some volume; that volume might not be ideal for a chemical reaction, all the time.

If the chemical energy is transfered to electrial, the electromagnetic motor as all the energy available, perhaps pre-stored in a battery, and can apply full torque to a stopped wheel without the wheel having any feedback on the amount of energy that the electrical generator applies.


That's how I read it at least.
 
When looking at a star in the SIMBAD astronomical database, how do I figure out how far away from Sol the star is, in light years, using the data on the screen?
 
Is there an upper limit to frequencies? I.e. is there n such that nothing can happen in frequency greater than n Hz?
 
Cheezy the Wiz said:
I have an engineering question.

I'm reading about Diesel-Electric locomotives, and the article mentions that they were favored over purely petro-fired engines because only electric motors are capable of supplying full torque at 0 RPM. I do not understand this statement. Why are electric motors uniquely capable of this and why is this desirable in a train locomotive?
Click to expand...


All internal combustion engines have a range of RPMs where they supply the high end of torque that the engine is capable of. And it is never near zero. The engine has to be at at least its medium RPM range. Cars and trucks work with that problem by having a transmission with multiple gears, so that in low gear the engine is turning at a higher speed and delivering more torque. In high gear the speed of the engine is lower compared to the speed of the car. If you know how to drive a manual transmission car then when you were learning you learned what happens when you release the clutch too fast. The motor stalls. Same if you try to start from a dead start in high gear. The reason is that the motor does not have enough torque to overcome the inertia of the car. You need a lot of torque to overcome sitting still and getting moving. You need less to maintain speed or have a minor acceleration. The mechanical connection from the motor to the wheel forces the engine to stop. That can potentially damage the engine if it's done too much.

Now consider the weight of a train. A clutch and transmission that could do that for a train would be huge and expensive.

An electric motor on the other hand has about the same torque over the whole speed that it is capable of. So you have that torque at standing still, which is where it is needed most.
 
PlutonianEmpire said:
When looking at a star in the SIMBAD astronomical database, how do I figure out how far away from Sol the star is, in light years, using the data on the screen?
Click to expand...

Provide / link an example.
 
GoodGame said:
http://en.wikipedia.org/wiki/Diesel-electric_transmission
It sounds to me that what the wikipedia article is saying is that a piston of a combustible engine that is attached to wheel axle (where the engined torque is applied) is stymied by the amount of expansion of the piston. With combustion as the source of the torque, the energy is supplied by a chemical reaction which is under physical constraints (V, T, P) and if say the wheel were stuck, the piston would be stuck so that the combustion chamber was at some volume; that volume might not be ideal for a chemical reaction, all the time.

If the chemical energy is transfered to electrial, the electromagnetic motor as all the energy available, perhaps pre-stored in a battery, and can apply full torque to a stopped wheel without the wheel having any feedback on the amount of energy that the electrical generator applies.


That's how I read it at least.
Click to expand...

Cutlass said:
All internal combustion engines have a range of RPMs where they supply the high end of torque that the engine is capable of. And it is never near zero. The engine has to be at at least its medium RPM range. Cars and trucks work with that problem by having a transmission with multiple gears, so that in low gear the engine is turning at a higher speed and delivering more torque. In high gear the speed of the engine is lower compared to the speed of the car. If you know how to drive a manual transmission car then when you were learning you learned what happens when you release the clutch too fast. The motor stalls. Same if you try to start from a dead start in high gear. The reason is that the motor does not have enough torque to overcome the inertia of the car. You need a lot of torque to overcome sitting still and getting moving. You need less to maintain speed or have a minor acceleration. The mechanical connection from the motor to the wheel forces the engine to stop. That can potentially damage the engine if it's done too much.

Now consider the weight of a train. A clutch and transmission that could do that for a train would be huge and expensive.

An electric motor on the other hand has about the same torque over the whole speed that it is capable of. So you have that torque at standing still, which is where it is needed most.
Click to expand...

Thanks a bunch guys! Learning this kind of stuff makes me wish I hadn't abandoned engineering for history back in college...it sounds so...useful and productive!
 
Status
Not open for further replies.

Similar threads

B
Vassal Questions
Replies
1
Views
342
antimony
A
Gori the Grey
Splitting a new thread off from an existing one
Replies
3
Views
677
Aiken_Drumn
Aiken_Drumn
V
TSG 238 Announcement
Replies
5
Views
2K
lerrocco
L
V
  • Sticky
TSG 242 Announcement
Replies
3
Views
633
Megalou
Megalou
V
TSG 240 Announcement
Replies
5
Views
921
gerishnakov
gerishnakov
Top Bottom