Talk:Cross product/Archive 3

Archive 1

Archive 2

Archive 3

Elegant alternative derivation?

Sentence removed from section "Matrix notation"

An elegant, alternative derivation is based on an isometric sketch of (x,y,z) axes with the (x,y,z) components of each vector (A,B) drawn parallel to the corresponding axes. The resulting formula for the constituents of the cross product (C = A x B) then appears by inspection, provided we are careful to take all orthogonal cross products in the order A:B (such as Az x Bx). For example, this method yields the magnitude (Cz = AxBy - AyBx) for the vector component along the z-axis and unit vector (k).

I removed this sentence from section "Matrix notation", as it does not seem to add useful information (Cz = AxBy - AyBx is already provided, with different notation, in the previous section), it is so badly written that I cannot understand its meaning ("The resulting formula ... appears by inspection"?), it does not seem to belong in that section, and uses a notation (Ax, Ay, Az...) which is not consistent with the rest of the article. Possibly, it sloppily refers to the demonstration already given in the previous section. If you know what it means and if you think it means something that is not already explained in the article and deserves to be explained, please rewrite it so that everybody can understand, and find or create a more appropriate section to contain it. Paolo.dL (talk) 17:16, 26 March 2012 (UTC)

Proposed mnemonical illustration

Here is something created in the process of this.

I hope this may help, but it may not be very good...

Illustration to find the cross product components: the clockwise arrows follow cyclic permutations of x, y, z in alphabetical order.

Opinions? Sorry about the notation but the basis notation (e_x, e_y, e_z) is clearer than (i, j, k) since these are also used for quaternions, and the e notation has clear extension to any other general curvilinear coordinates. F = q(E+v×B)⇄ ∑_ic_i 13:49, 28 June 2012 (UTC)

I may be getting it confused, but it seems to me that the sign is wrong. I'm not too sure I'd use this mnemonic myself. — Quondum^☏ 10:43, 29 June 2012 (UTC)

Fixed, but I don't care much. F = q(E+v×B)⇄ ∑_ic_i 13:21, 30 June 2012 (UTC)

I also don't see it being used much: it requires you to recall quite a lot (the layout of the forumula, the arrows) to recall something that is remembered easily directly (with the obvious permutation rules). Besides it's not really something that can be included as it's OR. Generally we don't include mnemonics unless they are notable themselves, i.e. if very well known such as SOHCAHTOA. There are simply too many otherwise, with everyone having their favourite.--JohnBlackburne^words_deeds 13:30, 30 June 2012 (UTC)

It looks like puke on the floor [1]. Why would anyone use this?? Agreed with User:JohnBlackburne and Quondum. Then again - it seems on many pages User:JohnBlackburne dislikes many things [2][3][4] - of course he would not like the analogy (but who would anyway)?? :-( Hublolly (talk) 00:15, 6 July 2012 (UTC)

Good for you. =( Please do NOT antagonize User:JohnBlackburne who is a good faith editor (those links show it), and please do NOT personally attack people like you did to Quondum - that was atrocious and as far from funny as could be..., and please do not edit other peoples comments. [5] =( ...

Both editors have a phenomenal amount of knowledge on maths and physics - far greater than mine, and are far more productive and constructive and valuable editors to the encylopedia than I am. =) F = q(E+v×B)⇄ ∑_ic_i 00:24, 6 July 2012 (UTC)