Wikipedia:Reference desk/Archives/Science/2015 November 7

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November 7

I will be correct if I say that the definition of “dimension” is “something that we can measure” ?

Will I be correct if I say that when we say “dimension” it means “something that we can measure”? (in oxford dictionary is written “A measurable extent of a particular kind, such as length, breadth, depth, or height”, but it's important for me to know the answer to the other definition) 78.111.186.226 (talk) 02:47, 7 November 2015 (UTC)

It originally meant "a measuring out".[1] It has become specialized to mean other things, like "a component of a situation", or in geometry, an object with "length, width, height" etc. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:01, 7 November 2015 (UTC)

Thank you for you answer, but I really didn't understand the answer for my question. (If the represented definition is considered as correct or no) 78.111.186.226 (talk) 06:18, 7 November 2015 (UTC)

You don't say in what context you are using the word. The OED has the geometrical definition "A mode of linear measurement, magnitude, or extension, in a particular direction; usually as co-existing with similar measurements or extensions in other directions.", but you have asked the question at the science desk, so perhaps you want Joseph Fourier's definition in Théorie anal. de la Chaleur (1822): "The power to which any one of the fundamental quantities or units is raised in the expression defining a derived quantity or unit in terms of them; also (in pl.), all the fundamental quantities in such an expression, each raised to its appropriate power, which together show how the unit of the derived quantity depends on the fundamental units; method of dimensions, dimensional analysis". The OED adds: "The ‘fundamental quantities’ are usually taken to be mass, length, and time, with the addition of one or more other quantities in certain cases (such as electrical and magnetic phenomena)". If you want a very simple definition for basic science, then your “something that we can measure” serves your purpose well. Dbfirs 08:18, 7 November 2015 (UTC)

The definition (in science & mathematics) is rather subtle. We talk about space as having "three dimensions" with time being a fourth dimension - but it's a bit more subtle than the concept of space having an X, a Y and a Z "dimension" because we're trying to describe a deeper "three-ness" of space. You could, for example, define a position in space by two angles and a scalar distance along that direction (polar coordinates) instead of X,Y and Z...there is nothing fundamental about there being three orthogonal distance axes. We routinely describe positions on our planet by latitude, longitude and altitude - but there are still three independent numbers used in the description. You could also describe a position by distances from three fixed points. But you soon find out that you always need exactly three numbers to specify a point uniquely. You never need four numbers and two is never enough. So the concept that space has "three dimensions" is somehow independent of how you choose to measure positions within that space. This deeper concept of "dimensionality" is somehow more fundamental than specific measurements.

We can also think of other weird and wonderful "spaces". As a computer graphics guy, I'm often thinking in "Color space" - which is similarly three-dimensional (Red, Green and Blue - or Hue, Saturation and Value - are commonly chosen axes). It's sometimes possible to solve problems by treating other quantities such as mass or electrical charge as if they were "dimensions" and to explore concepts such as mass/time/pressure/temperature as a four dimensional space. This leads us into concepts such as Dimensional analysis in which measurements of properties such as mass and charge are considered independent "dimensions". Then there are ideas like phase space where there are insane numbers of dimensions. SteveBaker (talk) 15:05, 7 November 2015 (UTC)

Basebull Bugs, according to what I got from you, I can say that Dimension is every type of measuring such length, width, depth, time and so on. Do I understand you well? 78.111.186.167 (talk) 00:46, 8 November 2015 (UTC)

Question about bees

Hello,

Can you tell me what articles would best provide me information on the decline of honeybee populations in recent years? — Preceding unsigned comment added by 2602:306:314C:CC80:87F:DF39:2EB1:F6F4 (talk) 05:58, 7 November 2015 (UTC)

If you mean wikipedia articles, see Colony collapse disorder and perhaps Pollinator decline. There are a bunch of related sub articles which will be linked from there e.g. Pesticide toxicity to bees, Imidacloprid effects on bee population, Bees and toxic chemicals, Diseases of the honey bee. Nil Einne (talk) 06:37, 7 November 2015 (UTC)

If you mean "Wikipedia articles", colony collapse disorder is the main article. --71.119.131.184 (talk) 06:36, 7 November 2015 (UTC)

Neonicotinoid#Decline_in_bee_population has some timely info and refs as well. SemanticMantis (talk) 23:00, 7 November 2015 (UTC)

What is the difference between axis and vector?

I'm trying to understand the main difference between them. Is the difference that the vector has a direction while an axis doesn't have? 78.111.186.226 (talk) 06:20, 7 November 2015 (UTC)

Without an example or reference, I would presume the difference is magnitude. A vector has a defined magnitude while an axis can be infinite. From Despicable Me, we know the nerd name "Victor" was replaced by "Vector" because his crimes had both Direction and Magnitude. Axis have direction but the magnitude is indeterminate. The units are immaterial so an X axis of force has the direction component, but in can support multiple vectors of varying magnitude. Superposition can determine the final vector on an axis but the axis is really only a direction (a scalar). --DHeyward (talk) 07:39, 7 November 2015 (UTC)

They are entirely different things. An axis is defined with respect to a coordinate system -- it is a set of points all of whose coordinates except one are zero. A vector is an entity that has magnitude and direction -- the exact definition varies according to context, but none of the widely used definitions give you anything resembling an axis. Looie496 (talk) 13:23, 7 November 2015 (UTC)

I disagree with Looie's definition of an "axis" - for example, I might talk about the "axis of rotation" of a spinning body or an "axis of symmetry" - in which case the axis has a position and a direction - but no magnitude. In the case where we're discussing one of the axes of a graph, then that Looie's definition happens to work - but it's not true for other uses of the word in physics and mathematics. I agree with DHeyward that the difference between a vector and an axis is that a vector has magnitude and an axis is presumed to be infinite in extent. Both need a position and a direction. However, people often talk about an "infinite vector" which fits the definition of an "axis" too. SteveBaker (talk) 14:47, 7 November 2015 (UTC)

You are right. I'm so sorry for that. I meant to the axis of anatomical plan. 16:06, 7 November 2015 (UTC) — Preceding unsigned comment added by 78.111.186.3 (talk)

Transformer Core Lamination Thickness

What would be an ideal thickness of a lamination used for stacking the core of a 50HZ 1kVA transformer? Is there any rule or formula which can be used to determine the thickness or number of laminations that a core will be split into in order to reduce eddy current losses?--Adenola87 (talk) 09:35, 7 November 2015 (UTC)

It is more of a cost cosideration. Thiner the better but more the cost. This explains the math:

[2] Page 42. You might notice too that US made transformers, although certified as OK on European voltages, never the less run hot. The US main frqueetcy is 20% higher than in the US so are less efficent. Thus, the greater losses producing more heat. So the best thinness is a trade off according to the application.--Aspro (talk) 14:40, 7 November 2015 (UTC)

@Aspro:, you will probably want to clarify your last statement. μηδείς (talk) 17:30, 7 November 2015 (UTC)

The last statement is explained in the reference. The one before is reinforced here [3]--Aspro (talk) 18:18, 7 November 2015 (UTC)

I was referring to "The US main frqueetcy is 20% higher than in the US" which is an apparent contradiction. μηδείς (talk) 21:31, 7 November 2015 (UTC)

It's 20% higher than in the UK, of course (60Hz vs. 50Hz.) Dbfirs 21:35, 7 November 2015 (UTC)

"Laminations for small power transformers are generally 0.014 inch thick; thicker laminations up to 0.025 inch are occasionally used, but result in increased losses..." - page 235, Radiotron Designer's Handbook, Fourth Edition, 1952, which is available online as a free PDF download. I would think a 1 kVA power transformer would fall into the 'small' class. Therefore, the thickness of your laminations ought to be in the vicinity of 0.015 inch. Akld guy (talk) 02:11, 8 November 2015 (UTC)

I just opened-up a a burnt-out transformer from an old AVR and measured the thickness of the laminations. Yes, @Akld guy you are right, it is just within the range you mentioned. I am currently working on a special project I appreciate the help that I am getting here. Thanks.--Adenola87 (talk) 10:14, 9 November 2015 (UTC)

Chairlift height and accidents

How high to the ground (not the altitude) can a chairlift go? Has anyone been forgotten in one and died because he couldn't get down? This is the plot of Frozen (2010 American film), which is unrealistic, but I wonder how accidents in chairlifts happen. The corresponding article does not have any reference of deadly accidents. Denidi (talk) 14:32, 7 November 2015 (UTC)

Close; I found Money-burning snowboarder rescued from Alpine ski lift. He was trapped 10m up when the ski lift shut down for the night and was only found 6 hours later when he burned 120 euros of banknotes to attract attention. Alansplodge (talk) 01:35, 8 November 2015 (UTC)

In researching this, I did find [4] which claims a death in the short lived Charlotte Pass to Thredbo ski lift in Australia, but it doesn't seem very confident and I couldn't find more info because a lot of sources are discussing how the lift was dangerous due to the risk of death from exposure and inaccessbility of the terrain meaning rescues were difficult.

I suspect deaths from being left behind are less common than death from falling or not offloading safely, or maybe also some cases off being stuck somehow and fatally injured; whether due to operator error, user error or defective lifts. E.g. [5] [6] [7] [8] [9] [10] suggests deaths from falling are uncommon in the US, but they do happen. Note the statistics on deaths only refer to cases of defective lifts, although I guess you may wonder whether cases where someone has a medical emergency on a ski lift which is why they fall like [11] [12] should be called a death from a skilift. [13] [14]is a case of being stuck and tangeled in a backpack and strangled, in the French Alps. [15] a death from a fall in it Italy. [16] in the Swiss alps is a death from falling. [17] is interesting, a death from falling but only after not dismounting at the right time, also in the Swiss alps. Not sure whether you'll consider them ski lifts but [18] mentions two deaths on a Surface lift#Magic carpet. There are also case like [19] where someone is killed perfoming maintenence ([20] has a case where someone lost both legs). There are also cases like [21] where some hits a lift tower, but I guess most wouldn't consider them deaths due to ski lift accidents. [22] has some general comments on safety in the US.

Nil Einne (talk) 02:58, 8 November 2015 (UTC)

Whoops somehow I missed that you said chairlift rather than skilift, sorry. I think even discounting the Magic carpet case, some of those were ski lifts of some sort but not chair lift. I'm lazy to check each one and I'm not sure if the sources I provided always specify. Since you did mention chair lift, there is a disputed claim of a death on the former Skylink chair lift at Dreamworld in Australia here [23], but while I'm fairly confused about what other thread is being referred to, I'm inclined to believe the death didn't happen because I can't find any mention of it anywhere which even if it happened in the largely preinternet age, I find unlikely. I did find another mention of the accident (which if the description in the other forum is correct was due to user error) here [24]. Nil Einne (talk) 05:11, 8 November 2015 (UTC)

Some of them are chairlift accidents, but it seems that someone, either a rider or an operator, has to do something really stupid to cause the accident.--Denidi (talk) 12:05, 8 November 2015 (UTC)

Which of this definitions is the correct with respect to this axis?

Which of these 9 definitions of axes, that mentioned in Merriam-Webster dictionary, is correct with respect to the axes that draw anatomy plans? 78.111.186.3 (talk) 14:56, 7 November 2015 (UTC)

The longitudinal axis would fall under 1b and 1a. Sagittal axis would be 1a. Some pictures include a 'frontal axis' and that is less clear to me... perhaps number 9 or number 5? 99.235.223.170 (talk) 15:30, 7 November 2015 (UTC)

(ec) That would be 1(d): "one of the reference lines of a coordinate system" - in anatomical drawing, the axes are broadly named (Anatomical_terms_of_location#Axes) Anterior/Posterior, Dorsal/Ventral and Sinester/Dexter...but when the drawing is of a limb that can rotate and therefore be aligned in various ways, separate terminology is applied (Medial/Lateral and Proximal/Distal). SteveBaker (talk) 15:33, 7 November 2015 (UTC)

You are probably correct. FWIW, I'm more used to referring to them all as 'planes', though my anatomy schooling is long behind me. 99.235.223.170 (talk) 19:04, 7 November 2015 (UTC)

The acceptable names for the axes

Do these letters indeed represent these measures as follow?

X – measures the width

Y – measures the length

Z – measure the depth

20:44, 7 November 2015 (UTC) — Preceding unsigned comment added by 78.111.186.167 (talk)

I would swap round X and Y, and use "height" if the Z axis goes upward, but conventions vary. Lower case letters x, y and z are normally used for the measurements, with capital letters being reserved for the axes. Dbfirs 20:58, 7 November 2015 (UTC)

Convensions vary from places to places. Z will be the most likely the less relevant of the 3 dimensions. If you are drawing a map, you might as well forget the heights, so Z will be height. If you are writing a 3D engine for a game however, you might think of X and Y the width and the height to fit the monitor view point and make Z the depth. So It depends.

Also, I just noticed you used the word "length". While it would be the right word if you were describing a pool, I'd rather use "height" most of the time to avoid confusion. Iluvalar (talk) 22:23, 7 November 2015 (UTC)

... that would be the answer on the computer help desk, but the words associated with the axes are just conventional. You can choose whatever seems best for your application, and you can rotate the axes as you wish. Dbfirs 22:40, 7 November 2015 (UTC)

Length, width, height, depth, and breadth are five of the common words we use in English to describe three spatial dimensions. You can also throw in an "ana_(mathematics)" or "kata" if you want to talk about four. So there's not a one-to-one function that maps the words to the dimensions, and no unique "best" choice. If you're dealing with a Hilbert space such as a frequency domain, you need infinitely many dimensions, so we just call them something like ${\hat {f}}_{1}\ldots {\hat {f}}_{n}\ldots$. As Dbfirs says, this is just convention, and there's no one "right" assignment, though the one you give is indeed fine and common, and acceptable :) SemanticMantis (talk) 22:58, 7 November 2015 (UTC)

How to describe 2D

I have two options two describe 2D positions (maybe you have more and better): 1) "Each position can be described as a result of two axes". 2) "Each position can be presented by two different axes." 78.111.186.167 (talk) 23:36, 7 November 2015 (UTC)

Try "Each position can be uniquely described by coordinates along two perpendicular axes". StuRat (talk) 00:42, 8 November 2015 (UTC)

Note that they don't have to be perpendicular, as long as they're not parallel. Tevildo (talk) 02:40, 8 November 2015 (UTC)

I suppose, but it doesn't seem very practical to use such a system. StuRat (talk) 08:03, 9 November 2015 (UTC)

See Nomogram for some examples of non-perpendicular (and, indeed, parallel) axes. Tevildo (talk) 08:37, 9 November 2015 (UTC)

That does not satisfy the condition that each position is uniquely described by coordinates along two axes - each point on the central axis can be represented by an infinte number of pairs of coordinates on the other two axes (corresponding to lines of different angles through the point). MChesterMC (talk) 09:50, 9 November 2015 (UTC)

These questions are confusing. What is it that you don't understand about one, two and three dimensional geometry? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:21, 8 November 2015 (UTC)

Now I understand it well. Thank you. 78.111.186.167 (talk) 06:11, 8 November 2015 (UTC)

I think the axis stuff is confusing. Here's a simple approach: a 1-D object has length only; a 2-D object has area only; a 3-D object has volume. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:48, 8 November 2015 (UTC)

Silicone sealant for DIY waterproofing.

It is possible to prepare a mixture for waterproofing fabric by mixing together white spirit and the right kind of silicone caulk/sealant. The right kind of silicone sealant is one that does not smell of acetic acid. It cures differently. One such product is GE Silicone II but this is relatively expensive where I live. Could someone tell me whether [this product called Silirub 2] would be suitable? It's chemically neutral although it still requires moisture to cure, according to that specification sheet. — Preceding unsigned comment added by 78.148.104.242 (talk) 23:59, 7 November 2015 (UTC)

A neutral sealant like this does seam better for your application on fabric. As to the best activator in order to get it to cure properly and as to whether this product will obtain the desired results. I would contact the UK distributor here: [25] Then tell them your application, and ask them if their product is suitably and how to apply it etc. I'm wondering is your trying to waterproof something like the hood on top of say a VW Campervan in which case it is better (and cheaper) to buy the finished fabric or maybe a liner for a pond? Intrigued - do please tell. I may been there all ready and got the tee-shirt. --Aspro (talk) 12:14, 9 November 2015 (UTC)