0199: "Right Hand Rule"

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0199: "Right Hand Rule"

Postby Babbler » Wed Dec 20, 2006 5:38 am UTC

I remember learning about the right hand rule, wondering what to do if your missing a right hand. I believe this comic fill in that gap in our educational sytem

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Postby Peshmerga » Wed Dec 20, 2006 5:39 am UTC

Females can look at porn too!

And they do! Or so I'm told.
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Postby Gelsamel » Wed Dec 20, 2006 5:50 am UTC

Couldn't females just be in a cold room for that?

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Postby Babbler » Wed Dec 20, 2006 6:00 am UTC

Gelsamel wrote:Couldn't females just be in a cold room for that?

Or they could pore cold water on the shirts.

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Postby digitrev » Wed Dec 20, 2006 6:10 am UTC

Babbler wrote:
Gelsamel wrote:Couldn't females just be in a cold room for that?

Or they could pore cold water on the shirts.

Wet T-shirt contest?
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Postby tiny_sparks » Wed Dec 20, 2006 6:18 am UTC

I would think that watching porn or performing a wet t-shirt contest would be counteractive to the original purpose of solving a vector.

Unless you're REALLY good at not getting distracted.

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Postby Gelsamel » Wed Dec 20, 2006 6:25 am UTC

What would we be distracted by? :D

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Postby tiny_sparks » Wed Dec 20, 2006 6:32 am UTC

Well, I have a pretty short attention span, so I would probably become much more interested in figuring out the average growth velocity of my assets, etc. :)

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Postby EvanED » Wed Dec 20, 2006 6:43 am UTC

"Hey baby, wanna go back to my place and help me multiply vectors?"

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Postby aldimond » Wed Dec 20, 2006 7:14 am UTC

EvanED wrote:"Hey baby, wanna go back to my place and help me multiply vectors?"


"Oh, no, I don't seem to see anything there! Did you accidentally take the dot product of those orthogonal vectors instead of the cross-product?"
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Postby hyperion » Wed Dec 20, 2006 7:56 am UTC

[begin stupid]
umm...what exactly is the right-hand rule?
the wiki article didn't help
[end stupid]
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Postby skeptical scientist » Wed Dec 20, 2006 8:04 am UTC

Is there such a thing as a "tightly closed" space? If so, what is it?
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Postby Babbler » Wed Dec 20, 2006 8:07 am UTC

HYPERiON wrote:[begin stupid]
umm...what exactly is the right-hand rule?
the wiki article didn't help
[end stupid]

Go look it up at a linear algebra textbook.

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Postby Torn Apart By Dingos » Wed Dec 20, 2006 11:30 am UTC

HYPERiON wrote:[begin stupid]
umm...what exactly is the right-hand rule?
the wiki article didn't help
[end stupid]

By convention a 3D graph is drawn like this (but it can be rotated so that, for example, the y-axis goes inwards instead):
Image
A way to remember this is to extend the first three fingers in your right hand and then the x-axis will be your thumb, the y-axis your index finger and the z-axis your middle finger.

Similarly, it'll help you remember the direction of the resulting vector of a cross product, if your thumb is a and your index finger is b in this image:
Image

And the direction of curl/rotation:
Image

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Postby EvanED » Wed Dec 20, 2006 3:21 pm UTC

HYPERiON wrote:[begin stupid]
umm...what exactly is the right-hand rule?
the wiki article didn't help
[end stupid]


It also can help you figure out which way you have to turn something like a screw or a light-bulb. Point your thumb in the direction you want it to go, then the direction your fingers naturally curl is the way to turn it.

This is why most screw threadings (that are used in the US anyway) are called right-handed. Naturally, if you have something with a left-handed threading, this will give you exactly the wrong answer.

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Postby no-genius » Wed Dec 20, 2006 3:33 pm UTC

EvanED wrote:It also can help you figure out which way you have to turn something like a screw or a light-bulb. Point your thumb in the direction you want it to go, then the direction your fingers naturally curl is the way to turn it.


Easy! righty-tighty, lefty-loosey!
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Postby tiny_sparks » Wed Dec 20, 2006 5:28 pm UTC

I learned the right-hand rule in physics. I never did get it right.

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Postby athelas » Wed Dec 20, 2006 5:46 pm UTC

Yeah - according to physics teacher, in every large-scale E/M exam you'll see someone trying to apply the left-hand rule.

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Postby wisnij » Wed Dec 20, 2006 6:03 pm UTC

athelas wrote:Yeah - according to physics teacher, in every large-scale E/M exam you'll see someone trying to apply the left-hand rule.

My physics teacher in high school says he's seen kids right-hand-rule themselves out of their chairs during the AP tests.
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Postby FiddleMath » Wed Dec 20, 2006 6:31 pm UTC

EvanED wrote:It also can help you figure out which way you have to turn something like a screw or a light-bulb. Point your thumb in the direction you want it to go, then the direction your fingers naturally curl is the way to turn it.


Thank you! You just saved me about 5 seconds every time I pick up a wrench! (After all, it's obviously worse to try it in both directions, and get it wrong once, than to waste time rotating a bolt in your mind.) :D

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Postby Antipas » Wed Dec 20, 2006 7:51 pm UTC

This "right-hand rule" is just another right dominance conspiracy against the left-handed population.

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Postby EvanED » Wed Dec 20, 2006 8:14 pm UTC

no-genius wrote:
EvanED wrote:It also can help you figure out which way you have to turn something like a screw or a light-bulb. Point your thumb in the direction you want it to go, then the direction your fingers naturally curl is the way to turn it.


Easy! righty-tighty, lefty-loosey!


That makes no sense! What way is right? There are equal amounts of the screw that have a leftward trajectory as a rightward trajectory at any given moment! Bah!

(I usually get it right if someone says "turn it [left|right]", but only if I work on instinct and don't give it any thought. If I start thinking about it, I confuse myself.)

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Postby EvanED » Wed Dec 20, 2006 8:15 pm UTC

FiddleMath wrote:
EvanED wrote:It also can help you figure out which way you have to turn something like a screw or a light-bulb. Point your thumb in the direction you want it to go, then the direction your fingers naturally curl is the way to turn it.


Thank you! You just saved me about 5 seconds every time I pick up a wrench! (After all, it's obviously worse to try it in both directions, and get it wrong once, than to waste time rotating a bolt in your mind.) :D


Exactly.

P.S. I assume that the phrase "code sandwich" means something to you? :-p

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Postby aldimond » Wed Dec 20, 2006 10:14 pm UTC

EvanED wrote:
no-genius wrote:
EvanED wrote:It also can help you figure out which way you have to turn something like a screw or a light-bulb. Point your thumb in the direction you want it to go, then the direction your fingers naturally curl is the way to turn it.


Easy! righty-tighty, lefty-loosey!


That makes no sense! What way is right? There are equal amounts of the screw that have a leftward trajectory as a rightward trajectory at any given moment! Bah!

(I usually get it right if someone says "turn it [left|right]", but only if I work on instinct and don't give it any thought. If I start thinking about it, I confuse myself.)


The situation where "left (counter-clockwise) = loose and right (clockwise) = tight" breaks down is with garden hoses.

Because you're screwing in a garden hose from the bottom but looking at it from the top the whole thing is reversed. But using the right-hand rule makes it work, because you stick your thumb up and see the fingers going counter-clockwise.

I mean, either that or you could just turn the whole universe clockwise around the garden hose, if that's easier. I guess it varies person-to-person. But yeah, the first time I tried to use a hose after learning that most screwing-in is done clockwise I spent about 15 minutes trying to turn the hose the wrong way before figuring it out. It was very confusing.
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Postby ian_evil » Wed Dec 20, 2006 11:19 pm UTC

Where were these rules developed? Experimentation? Have they been tested? Was someone shooting a hand gun and/or watching porn when suddenly they discovered these new rules in vector multiplication?

God forbid I ever go back to college, but if I start blasting off shots from my .50 in 3D Geometry and the math doesn't add up with these new proposed rules, I'm gonna be pretty pissed ... and have a gun.

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Postby Torn Apart By Dingos » Wed Dec 20, 2006 11:48 pm UTC

ian_evil wrote:Where were these rules developed? Experimentation? Have they been tested? Was someone shooting a hand gun and/or watching porn when suddenly they discovered these new rules in vector multiplication?

God forbid I ever go back to college, but if I start blasting off shots from my .50 in 3D Geometry and the math doesn't add up with these new proposed rules, I'm gonna be pretty pissed ... and have a gun.

It's just convention. The cross product of two vectors can be defined in one of two ways, and one was chosen.

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Postby aldimond » Thu Dec 21, 2006 12:43 am UTC

And clearly the convention was chosen by a person that masturbates left-handed.
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Postby ghlmtz » Thu Dec 21, 2006 1:01 am UTC

Antipas wrote:This "right-hand rule" is just another right dominance conspiracy against the left-handed population.


Actually, as my math teacher explained, it isn't. You see, on tests and such most people (the right-handed ones) will be going along fine, but when they come to a problem that uses the rule, they have to put down their pencil and fiddle with their hand. Us left-handers, however, have efficiency on our side and can continue gripping the pencil while figuring out the vector orientation. I'd like to shake hands (with my left, naturally) with the left-hander who came up with this rule.

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Postby Babbler » Thu Dec 21, 2006 2:13 am UTC

aldimond wrote:And clearly the convention was chosen by a person that masturbates left-handed.

When it comes to masturbation, everybody ambidextrous.

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Postby Ronfar » Thu Dec 21, 2006 2:59 am UTC

Where can I find this "noncartesian porn" of which you speak?
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Postby muteKi » Thu Dec 21, 2006 6:26 am UTC

I like how "tightly closed nonorientable spaces" works as a really lame pun.

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Postby AwesomesauceOnCeilingfish » Thu Dec 21, 2006 6:59 am UTC

I just have this wonderful mental image of someone whacking it and then grinning and saying "Hey look! I'm a result vector!"

Please tell me this is how you came up with the idea for this comic.
whatwhat

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Postby ohki » Thu Dec 21, 2006 9:03 am UTC

In before anyone starts talking about the magnitude of their vector.

Also, déjà vu:
sketerpot wrote:In order to solve the contentious issue of penises, I propose that penises be treated as vectors -- that is, they have a magnitude and a direction. They can be added together to form a larger penis that may be pointing in a different direction, and they can be multiplied by scalars.

As a simple consequence of this model, it becomes possible to define all possible penises as linear combinations of three linearly independent penises. Any penis should then be described by a function p(t) : R -> R^3 which returns a triple of real coordinates specifying the size and orientation of the penis at any given time t relative to a standard basis of three orthogonal penises.

Aw hell, I just wanted an excuse to turn penises into a vector field.
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Postby earcaraxe » Thu Dec 21, 2006 1:38 pm UTC

aldimond wrote:And clearly the convention was chosen by a person that masturbates left-handed.


Perhaps that's why this works as a good alternative to the right-hand rule.

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Postby digitrev » Thu Dec 21, 2006 4:32 pm UTC

Heh. To me, the right-hand rule has a completely different connotation. In high school, my physics teacher taught us with the left-hand rule, so that we would use electron flow instead of current flow. But, being the kinda guy he was, he told us what the right-hand rule was. He also told us that he had his own right-hand rule. Namely, if we touched anything on his table except for a pen or pencil, he'd smack us upside the head with his right hand. He kept a very tight right-hand rule over his class. Then one of the graduating physics classes gave him a right-hand rule stick. It was a hockey stick with a right-handed glove attached to the holding end. It was freakin' awesome.
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Postby meso » Fri Dec 22, 2006 2:11 am UTC

Ronfar: Non-cartesian Porn. Well, kinda.

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Postby RealGrouchy » Fri Dec 22, 2006 5:19 am UTC

I don't remember learning the right- and left-hand rules in high school, but I do remember being told to learn them.


As for garden hoses and lightbulbs, it's still consistent. You just have to imagine that you are looking at it straight on.

On a bicycle, one of the pedals is screwed in backwards (so that as you pedal, it always turns towards the tightening direction instead of the loosening direction). I can never remember which one it is, but looking at the back of the hole usually helps.

I also can never remember which way to turn to remove the freewheel/cassette or bottom bracket. Most of the rest of a typical (north-American, at least) bike follows the left-loosey, righty-tighty convention. They also use metric allen keys and wrench sizes for most of the parts.

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Postby Teaspoon » Fri Dec 22, 2006 5:50 am UTC

I believe the backwards thread would be for the starboard pedal.

The pedal stays level as the shaft it's mounted on the end of rotates around a port-axis, so the pedal's rotation is in the starboard direction. This would make the starboard pedal unscrew itself to starboard if it didn't have a left-handed thread.

I used port and starboard because there are as many definitions for "left" and "right" as there are directions you can look from.

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Postby Armentia » Fri Dec 22, 2006 6:40 pm UTC

I was always taught the phrase 'top-left-off'

With this, you just imagine looking straight on if you're not already, such as hooking up a gardening hose. Then, the top of the bolt, hose, etc, turning that left will produce an effect one would call 'unscrewing' or off. And for those who would be challenged in wondering how to get it back on, you could possibly also memorize 'top-right-on'

I always hated 'righty-tighty, lefty-loosey' because I thought about it too much and wondered, "right from the top or bottom? o.O"

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Postby chaosite » Sat Dec 23, 2006 10:47 pm UTC

I find the rules good and approve of them...

Except the book one.

See, here in Israel we're backwards. Literally, Hebrew is a right to left language, so the books open the other way around.

Otherwise, its great, you probably have a book with you everytime you try to find the product of two vectors.

I, too, have flunked a test for using the left handed rule instead of the right handed one... And when attempting to fire a rifle, I used it left handed and closed the left eye.

I'm "ambidextrous", but what it really means is that I'm confused.


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