Wikipedia:Reference desk/Archives/Mathematics/2023 September 21

Welcome to the Wikipedia Mathematics Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

September 21

Vocabulary Question

What exactly are the differences between the words "perpendicular", "normal", and "orthogonal"? I more or less use these words interchangeably, but I assume that they have precise definitions. Puzzledvegetable^{Is it teatime already?} 00:57, 21 September 2023 (UTC)

You can read perpendicular, Orthogonality, and Normal (geometry). They are pretty much the same, except that I think "normal" usually refers to vectors. Bubba73 ^{You talkin' to me?} 01:19, 21 September 2023 (UTC)

Perpendicular has to do with a string hanging straight down in the direction of gravity (perpendiculum = plumb line or plumb bob), typically at a right angle to the ground. Normal has to do with a right-angled stick (norma = carpenter's square). Orthogonal literally = right angled in Ancient Greek (came to English via French via Latin); the Latin analog is "rectangular". –jacobolus (t) 01:21, 21 September 2023 (UTC)

Each of these terms is used with several related but different meanings; the uses overlap, and which term is preferred in which context may be mostly a matter of tradition. One difference is that "normal" is often used as a noun ("the normal") and then refers to a one-dimensional object, while "orthogonal" is mainly used as an adjective and can apply to a pair of subspaces of a metric space that can have any dimensions. (Given an m+n-dimensional space, an m-dimensional subspace can be orthogonal to an n-dimensional subspace.) The geometric term "perpendicular" is mainly used in traditional Euclidean geometry.  --Lambiam 17:21, 21 September 2023 (UTC)

Curious about UTC-Time zone

I am wondering who I can contact to know more about UTC -LOCK and whether its related to covid emergency broad cast related to ism band specific to geographic location.

Thanks Shireesh Avenger (talk) 03:03, 21 September 2023 (UTC)

I have no idea what "UTC-LOCK" refers to, but I am pretty confident it is not a mathematical topic. We have articles on UTC and Time zone. neither of which contains the word "LOCK".  --Lambiam 17:05, 21 September 2023 (UTC)

A quick Google search for "UTC-LOCK" doesn't yield anything particularly useful. Rusty4321 ^{talk contributions} 23:56, 22 September 2023 (UTC)

Can you tell us something about the circumstances in which you came across the phrase "UTC -LOCK"? 88.111.190.170 (talk) 14:50, 29 September 2023 (UTC)