Physics question

[Umfriend]

OK, am I totally moronic?

My kid gets the following Q: It takes 170 liters of Nitrogen(gas) at room temp. to create 1 liter of liquid Nitrogen at -196C. How many times is the distance between the molecules reduced?

Help me guys, quick!

[white]At school they seem to think the distance between molecules is reduced 170 times[/white]

[dZeus]

170 l = initial volume (3 dimensions).
1 l = target volume

The volume has shrunk 1/170 to get to the new situation.
The question however is: what is distance factor between the two situations (in one dimension)?

Since they supply only the difference in three dimensions, the volume factor (1/170) needs to be converted into one dimension to get the distance factor.

170 ^ (1/3) = 5.53965825675

In the initial volume, the molecules are 5.53965825675 times as far from each other as in the target volume.

They might want to know the 1/ for this result, which is 0.18051655059

of course this is not entirely correct, as the nitrogen changes phases between the two situations, and its dynamics change a lot.

[Umfriend]

Thank you for this. 1st grade "brugklas"/"HAVO/VWO" and this is what they get in Science... The textbook (leaflet actually) only gives the question, not the answer, theory or methed, but my son says he is certain the teacher says the answer is 170 times....

On the one hand, my son has got to be wrong, on the other, education nowadays... I'll mail the teacher today and raise the question.

[dZeus]

Thank you for this. 1st grade "brugklas"/"HAVO/VWO" and this is what they get in Science... The textbook (leaflet actually) only gives the question, not the answer, theory or methed, but my son says he is certain the teacher says the answer is 170 times....

On the one hand, my son has got to be wrong, on the other, education nowadays... I'll mail the teacher today and raise the question.

Best check the handbook to see if this type of theory is dealt with (the power of 1 over X).

Might also be a tough question because you need to realise that it does not matter how many particles there are for the change in relative average distance between particles when the volume changes.

It could very well be a matter of a badly formulated question to which the answer should have been 170... I've seen those sometimes in (bad) books and more so with (bad) teachers coming up with their own questions.

[Umfriend]

There is no handbook. Just a crappy leaflet and whatever is discussed during class (of which my kid makes very little notes, that's on him). The question is as follows: "Je hebt 170 litel stikstof (kamertemperatuur) nodig om er 1 liter vloeibaar stikstof (-196 C) van te maken. Hoeveel keer wordt de afstand tussen de stikstofmoleculen kleiner?".

My kid must have understood wrong, very wrong, or I'm about to explode. It's not the first crappy shit I've seen on these schools.

[dZeus]

There is no handbook. Just a crappy leaflet and whatever is discussed during class (of which my kid makes very little notes, that's on him). The question is as follows: "Je hebt 170 litel stikstof (kamertemperatuur) nodig om er 1 liter vloeibaar stikstof (-196 C) van te maken. Hoeveel keer wordt de afstand tussen de stikstofmoleculen kleiner?".

My kid must have understood wrong, very wrong, or I'm about to explode. It's not the first crappy shit I've seen on these schools.

The question is indeed as you translated.

They have physics lessons without using a handbook!? wtf... that's a very bad sign!

[Umfriend]

In my time, physics didn't start until 2nd year and chemistry until 3rd year. But now they have this class called "Science" which is supposed to do all sort of things, a bit of physics, chemistry, biology and with an applied twist (electronics, making batteries from potatoes etc). It may not be such a bad idea but in my experience (I have an older daughter who finished high school already), it just basically does nothing substantial.

[dZeus]

In my time, physics didn't start until 2nd year and chemistry until 3rd year. But now they have this class called "Science" which is supposed to do all sort of things, a bit of physics, chemistry, biology and with an applied twist (electronics, making batteries from potatoes etc). It may not be such a bad idea but in my experience (I have an older daughter who finished high school already), it just basically does nothing substantial.

when I consider the changes made to the Dutch educational system in the last 30 years (maybe longer?) it seems that the politicians in charge seem hell bend on destroying it, for various justifications:
- modernization (let's teach children how to punch numbers into a calculator rather than understanding what the actual operations do). Same for computer usage.
- prestige (some never tested radical overhaul that can go into recoded history as being introduced by Politician X or Y). Never mind most of these changes aren't tested and usually seem to make things worse than they were before.

however, when compared to what I've seen so far here in France, the Dutch educational system is absolutely fabulous. Putting a child into a French school probably should count as a form of mental child abuse.

[UtwigMU]

Why is this going on everywhere? Here too education system is being "reformed" and quality dropped from 30 years ago.

[Umfriend]

OK, before we get into a frenzy, I can't ignore the very real possiblity that my kid has simpl;y misunderstood, he has that sometimes. Gonna mail the teacher.

[dZeus]

OK, before we get into a frenzy, I can't ignore the very real possiblity that my kid has simpl;y misunderstood, he has that sometimes. Gonna mail the teacher.

He misunderstood that they've changed the way physics, chemistry and biology is taught, and that there's no official handbook for this chimera?

[Umfriend]

The plot thickens. I asked the teacher the question by mail. The reply I got, through Google Translate, was: "The purpose of Section 3 is that the students are familiar with the concept of molecules and the behavior of molecules in the different phases. This model is of course somewhat simplified. This also applies to question 15. The importance of this question is that your son understands that when a substance is cooled, it occupies a smaller volume, and that there is less space between the molecules will sit (which the attraction between the molecules is greater). Your son should therefore the phases of materials, the movement of molecules, the space between molecules, the temperature of the substance and not the change of the molecules themselves may link to each other."

I originally asked for the answer to the question above, not the purpose of the section that actually had this question as an assignment. I am fine with the intent but if it is only concepts you want to bring across, then way ask for calculation? And besides, this takes a few weeks to explain? I am now seriously doubtful the teacher knows the answer... uhm....help?

[UtwigMU]

Well distance between molecules can be only average as there is Brown's movement going and molecules in liquid or gas form move all the time.

Didn't they learn the gas law pV = nRT

[dZeus]

are you sure the teacher is not a retired politician?

anyway, to say that there's 170 times as many molecules in the same volume is correct (density).

But to state the same for distance between molecules? imo that's flat out wrong

[Umfriend]

@UtwigMU: Sure and, no, they've not yet had Brownian motion or has laws, it's first grade high school. In fixed form, there is no brownian motion AFAIK and given most materials propensity to expand at rising temps the question perhaps is more relevant but even that has its caveats as in many structures, the distances between molecules differes based on the, uhm, " raster"/"grid". Even if you take 8 molceules where all are at the point of a virtual cube, the change in distance is not equal for all as bottom left front vs top right back, clearly closest neighbours, have the biggest change.

@dZeus: agreed.

I guess it is a weird question but that should not be solved by using idiotic answers. I've asked her to state the actual answer. Will let you all know.