[Mbodell]

kenberg, on 2013-April-13, 19:34, said:

barmar, on 2013-April-12, 11:14, said:

My related pet peeve: real estate tax rates in Massachusetts are specified per $1,000. Why not per 100, so they can just use percentages? I wonder if some anti-tax lobby had them do this, since it makes the taxes look larger if they have to say $13.61 instead of 1.361%.

Just as a guess, I would say that it is because prices are often phrased in terms of thousands. If the tax is $13.61 per thousand and the property is valued at three hundred thousand dollars, presumably just about everyone understands that the tax is calculated by multiplying $13.61 by three hundred. For some reason there are a lot of people who have a mental collapse when percentages are mentioned, even some who in other respects appear to be quite capable. If you tell them the tax is 1.361% of the valuation they will have to call someone in for a translation.

I think it is because a mil (1000th of a dollar) is the smallest amount of currency. It was actually called out as such in the 1786 Continental Congress and is still commonly in use for some utilities, property tax, gasoline, and the cash value of coupons. See Wikipedia article on Mill currency.

[barmar]

Mbodell, on 2013-April-14, 01:10, said:

Wow, I've literally never heard of that before in any math notation. Having coded a bit in lisp I'm completely fine with lots of nested ().

Good Lisp programmers use indentation to make the nesting more obvious, and use editors that assist in making the indentation match the parenthesis nesting level.

But when formulas are written linearly, in a font that doesn't allow for increasing size of parentheses, using different types of brackets makes the nesting clearer.

A number of Lisp implementations and dialects (e.g. Clojure) explicitly allow use of square brackets equivalently to parentheses.

[kenberg]

In Mathematica, [ ], ( ) and { } have totally different uses. Some, my wife for example, object. I think it is terrific..

[gwnn]

I would get a divorce.

[y66]

Divorce seems drastic but I understand it. Not making distinctions between [] () and {} is 1000x worse than saying tomahto instead of tomato. She probably doesn't like the Python programming language either.

[kenberg]

y66, on 2013-April-15, 10:31, said:

Divorce seems drastic but I understand it. Not making distinctions between [] () and {} is 1000x worse than saying tomahto instead of tomato. She probably doesn't like the Python programming language either.

I plan to learn Python. Right after I read Moby Dick. It's good to have long term plans.

[gwnn]

Physicists whining if anyone dares to measure 'weight' in kilograms yet happy to measure energy in kelvins, nanometers, cm^-1, ...

[mike777]

gwnn, on 2013-April-26, 00:59, said:

Physicists whining if anyone dares to measure 'weight' in kilograms yet happy to measure energy in kelvins, nanometers, cm^-1, ...

fwiw thought physicists all about measure...that was the main point.

now you say no

measure...contrast, compare

[gwnn]

http://www.colby.edu...em/Hartree.html
http://www.highpress...conversion.html

And a few other sites like this... Yes physicists like to measure but would it be too much to ask to use settle on the units? OK I usually work in atomic units but that's just to make the Schrödinger equation easier to write.

[kenberg]

gwnn, on 2013-April-26, 00:59, said:

Physicists whining if anyone dares to measure 'weight' in kilograms yet happy to measure energy in kelvins, nanometers, cm^-1, ...

Being an American, I never measure my weight in kilograms so this will make them happy? Weight, weight, don't tell me.

As for kelvin, it has been a while since I thought of such things. Looking it up on the Wikipedia led me to thermodynamic temperature, http://en.wikipedia....mic_temperature, where we find:

Quote

Temperature arises from the random submicroscopic vibrations of the particle constituents of matter. These motions comprise the kinetic energy in a substance. More specifically, the thermodynamic temperature of any bulk quantity of matter is the measure of the average kinetic energy of a certain kind of vibrational motion of its constituent particles called translational motions. find

"arises from" falls short of "is defined as". Nor does the rest really clear it up. I wouldn't expect a fundamental unit to be a ratio, but it must be. If you have twice as much substance, you don't have twice as much temperature so I guess it is average kinetic energy per atom or per mole or per something. But it also sounds as if only certain types of energy, the vibrational motion, is to be counted. Surely there is a precise defintion somewhere, but I am not seeing it in the Wik reference.

[Trinidad]

gwnn, on 2013-April-26, 00:59, said:

Physicists whining if anyone dares to measure 'weight' in kilograms yet happy to measure energy in kelvins, nanometers, cm^-1, ...

In my work I measure energy in eV (electronvolt). Particle physicists measure mass in eV (E=mc²). I would say that most physicists don't care so much whether people in everyday life measure their weight in kilograms or Newtons.

However, physicists do care that kids are taught the fundamental difference between mass and force. That works fine in the SI (metric) system. In the imperial (pound-foot-second) system this is problematic. The use of pounds as a unit of mass and a unit of force is confusing and that is plain ... well ... let's call it unfortunate.

I can easily imagine that -through a slip of the tongue- when talking to a colleague I might express mass in eV, but in a completely different way from the particle physicists (and my conversion from mass to energy is not linear).

Rik

_____________________________________________________________________________________

For those who might be interested (if not stop reading right here):
I work with an analysis technique called Low Energy Ion Scattering (LEIS). It is a technique for the chemical analysis of surfaces. In the analysis a light ion is aimed at the surface and collides with an atom at the surface of the sample (nothing nuclear or quantum physics, just two balls bouncing against each other).

These collisions at an atomic level are just like collisions between macroscopic objects: If I throw a tennis ball against a bowling ball, the tennis ball bounces back. If I throw a bowling ball at a tennis ball, the bowling ball does not bounce back. And a tennis ball thrown at a bowling ball will come back faster than a tennis ball that is thrown at a soccer ball. How fast the tennis ball is coming back depends on the mass of the tennis ball, the energy (or velocity) of the tennisball when I threw it and the mass of the ball that it bounces of. So, by measuring the energy (or velocity) of the tennis ball as it comes back, I can tell the mass of the ball that it bounced against.

In LEIS analysis, we know the mass of the ions that we are shooting at the surface and we know their energy (velocity). We then measure the energy they have after they have collided with the surface atom. If they come back with almost the same energy then they must have collided with a heavy atom (bowling ball). If they have lost a lot of energy they must have collided with a light atom (soccer ball). So, the ion's energy after the collision is a measure for the mass of the atom at the surface of the sample. In that way we can determine what elements are at the sample surface and how much there is of each element.

For the freaks I will give the equation that relates the mass of the surface atoms to the energy of the ions after the collision (just to show that it is not linear):

m_at=m_ion*(E_ion/E_o-2*sqrt(E_ion/E_o)*cos(alpha)+1)/(1-E_ion/E_o)

In this equation:
m_at= mass of the atom at the surface
m_ion= mass of the ion used in the analysis
E_ion= energy of the ion after the collision
E_o= energy of the ion before the collision
alpha = the angle between the ingoing and outgoing trajectory of the ion. If the ion flies straight, the angle is 0 degrees. If the ion comes right back, this angle is 180 degrees.

Our instrument measures the ions at an angle of 145 degrees. The standard analysis is performed by using He-ions (mass = 4 amu) with an energy of 3000 eV. Therefore, I could imagine that I would say to a colleague that Si (28 amu) has a mass of about 1700 eV whereas ¹⁶O has a mass of 1100 eV. Nonsense, of course, but my colleagues would understand what I meant.

[gwnn]

Boltzmann's constant times the temperature gives you the average kinetic energy (times some constant depending on the degrees of freedom.. I think) of particles. k_B*T is a good measure of what kind of transitions a particle can spontaneously perform. E.g. if you want to make two things stick together you will want the bonding energy to be much larger than k_B*T.

http://en.wikipedia....tzmann_constant

On topic: I hate people with umbrellas in crowded places. They should get shot immediately. Once we were singing the National Anthem in some open space and in the middle of the first stanza three drops of rain fell down. Everyone rushed to open their stupid umbrellas, thereby ruining the solemnity of the moment and, almost as bad, poking several people in the eyes.

[Trinidad]

gwnn, on 2013-April-26, 06:19, said:

On topic: I hate people with umbrellas in crowded places. They should get shot immediately. Once we were singing the National Anthem in some open space and in the middle of the first stanza three drops of rain fell down. Everyone rushed to open their stupid umbrellas, thereby ruining the solemnity of the moment and, almost as bad, poking several people in the eyes.

Was that in The Netherlands? In my experience the Dutch hardly* use umbrella's. They tend to use rain coats/suits instead.

Rik

* Hardly is relative. It rains often in The Netherlands.

[gwnn]

Sure Trinidad, but saying 'actually kilograms refer to mass and not weight' has always sounded elitist to me (apart from being wrong). Wouldn't it be better to start by saying 'in Physics, (...)'? Physicists do not get to define words (linguists also not). And this is even on top of the point that it is not even incorrect to talk about a force in terms of mass, space in terms of time, pressure in terms of length, ... Your relation between energy and mass is quite funny, though

edit: the umbrella story was in Romania.

[kenberg]

It is reasonable to hope that a student, before finishing high school, learns that his weight varies according to which planet he is on, his mass does not. I took this to be Trin's point regarding what physicists care about. It seems right. How important is it? Well, for a U.S. student maybe it's less important than knowing what happened in 1776, and more important than being able to recite Ode On a Grecian Urn from memory. But my views here may be influenced by my own knowledge of 1776 and my general vagueness about poetry in general and Grecian Urns in particular.

[gwnn]

It will only ever be important if he/she applies for the Mars mission.

Although Gamma Rays 101 might be of more immediate relevance in that case.

[GreenMan]

gwnn, on 2013-April-26, 06:45, said:

Sure Trinidad, but saying 'actually kilograms refer to mass and not weight' has always sounded elitist to me (apart from being wrong).

If anyone says this to me, I'll slug them.

[Trinidad]

GreenMan, on 2013-April-26, 12:31, said:

If anyone says this to me, I'll slug them.

I believe that, but with how many kilograms of force?

Rik

[GreenMan]

Trinidad, on 2013-April-26, 12:34, said:

I believe that, but with how many kilograms of force?

Rik

I dunno, 14.6 or so.

[mycroft]

Well, difference in weight between Enschede and Calgary (elevation 1000m, give or take) is measurable, but not noticeable. Between Enschede and Everest, maybe; but the other things that one would notice atop Everest would mean that the change in weight is a very low priority...