A thread for boring physics questions

Your cat? No no, you need a cat to untangle that.

That was a Samsung ad!?

It was??? How?

By the way, for your original question, you'll want to contact Jens Eggers at the university of Bristol, who has been investigating that very question for years. (that's a summary - they need a password for the full article, unfortunately)

oh, that URL at the end. Hadn't checked that before. Duh. (although it was pretty obviously videoshopped)

I would assume that this phenomenon is related to the fact that of the vast variety of topological configurations a strand or two of wire can be in, only one of those qualifies as "untangled," so anytime they move, tangling is what's going to happen. If you stop them from changing their topology, either with a tight coil and a twist tie or by putting them into a vacuum-sealed bag or whatever, then you can keep them from getting tangled. Any free movement (even uncoiling, as a musician you probably know this) will more than likely lead to at least one nice knotty fuckup.

Now the researchers have found that cables above a certain length have the same probability of getting knotted but that the time required to shake out a knot increases rapidly with cable length.

oh insipid conclusions, where would the grant process be without you?

Why isn't the heart heartshaped?

It's the same principal applied to why my fishing line becomes a birds nest when it even slightly comes into contact with other line.

Haha, this question has been bothering me for years, I'm glad to see proper scientific attention has been paid to it.

The scientific research here suggests that if you leave your shoes undone, they'll eventually tie themselves, providing the laces are long enough.

if they're made of headphone cable or fishing line yes

If you put an ice cube in a glass of water, does the level of the water go up, down or stay the same after the ice cube melts?

It will go down due to loss of water through evaporation, providing it's not stood outside in the rain.

Why isn't the heart heartshaped?

This used to concern me... but really, it is, kinda, if you ignore the aortas and stuff at the top. Pointing down to the right:

http://www.ynhh.org/cardiac/heart/exterior_heart_anatomy.jpg

If you put an ice cube in a glass of water, does the level of the water go up, down or stay the same after the ice cube melts?

I do interviews for physics undergrads at Oxford, and we love this question.

To first order, the level stays the same because, by Archimedes principle, the cube displaces exactly it's own weight of water (not volume). So when it melts and turns into liquid water, it takes up exactly the same volume it was displacing. This is easier to draw than it is to explain.

Any candidate who points out the second order effect gets good marks: the ice cube has the effect of cooling the water in the cup, so the density of the liquid water changes. If it starts above 4 C, e.g. room temperature, that means it contracts and the level falls very slightly. If it starts below 4 C (but above 0 C) it expands very slightly.

I like El Tomboto's explanation of tangling as a consequence of the Second Law.

You guys should listen to Naked Scientist podcast, it is always explaining hell of everything plus they take questions.

whoa i just interviewed an experimental particle physicist for an hour today and my brain is v full. it was a rad interview though! particles! energy!

http://answers.google.com/answers/threadview?id=108430

Can ants survive in microwaves? Yes. They find antinodes where the microwaves bouncing around cancel out, and they just chill there. Yaoow. Sounds like bullshit to me, but there's nothing on snopes and I have ants to conduct an experiment with.

I have no ants.

That is weird.

I threw ants in a microwave and none of them died when I turned it on for a few minutes (I don't recommend doing this btw). Next up in urban legends of animals in microwaves: I cook a chihuahua.

We have to put something bigger/slower than an ant in to prove the microwaves are powerful enough to kill something. It could be that anything can survive.

By "we" I mean Abbott and by "something" I mean maybe a dog.

Let's nuke Louis' new hairdo.

That urban legend about putting a Chihuahua in a microwave is seriously meant to dupe people who have never met the hate-filled tweakdogs. My friend's won't let her put it in her CAR.

Re: the original question:
http://www.eurekalert.org/pub_releases/2007-10/uoc--us100307.php

Based on these observations, the researchers proposed a simplified model for knot formation. The string forms concentric coils, like a looped garden hose, due to its stiffness and the confinement of the box. The free end of the string weaves through the coils, with a 50 percent probability of going under or over any coil. A computer simulation based on this model produced a similar pattern of simple and complex knots as observed in their experiments.

Smith and Raymer said that the model can also explain why confining a stiff string in a smaller box decreases the probability of knot formation. Increased confinement reduces the tumbling motion that facilitates the weaving of the string end through the coils. The paper cites other researchers who have proposed a similar effect to explain why knotting of the umbilical cord of fetuses is relatively rare, occurring only about one percent of the time. Confinement to the amniotic sac may restrict the probability of knotting.

Hmm.

Here's the paper: http://www.pnas.org/cgi/content/abstract/0611320104

It even has some movies, which are not awesome: http://www.pnas.org/cgi/content/full/0611320104/DC1

good thread

This is cool: http://www.nioz.nl/nioz_nl/281c18dbf72fc51c599b4f49dddc1143.php

http://cosmicvariance.com/wp-content/uploads/flocking_cover.jpg

http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_60/iss_10/28_1.shtml

Those are some terrific flocking photos.

I would assume that this phenomenon is related to the fact that of the vast variety of topological configurations a strand or two of wire can be in, only one of those qualifies as "untangled," so anytime they move, tangling is what's going to happen. If you stop them from changing their topology, either with a tight coil and a twist tie or by putting them into a vacuum-sealed bag or whatever, then you can keep them from getting tangled. Any free movement (even uncoiling, as a musician you probably know this) will more than likely lead to at least one nice knotty fuckup.

-- El Tomboto, Monday, September 17, 2007 6:20 AM (3 weeks ago) Bookmark Link

i agree with this, but technically, the whole point of topology is that it's invariant under continuous transformations, so you can't just change it willy-nilly

http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_60/iss_10/images/28_1fig2.jpg

There's topology and then there's topology.

I only grasp topology in terms of coffee mugs, solids and vast networks of machines, so forgive the misappropriation of the term from its mathematical usage. You know what I mean though.

yeah def i just wanted to sound like a big man

I only grasp coffee mugs and solids, and even then I drop them all the time. I broke my mug with all the different beers from Munich on it today. *96 tears*

http://www.nature.com/news/simulations-back-up-theory-that-universe-is-a-hologram-1.14328

http://www.nature.com/scientificamerican/journal/v15/n3/images/scientificamerican0206-74sp-I6.jpg

If you were floating in empty space and spun yourself around with your eyes closed, would you be able to tell that you were rotating?

http://en.wikipedia.org/wiki/History_of_centrifugal_and_centripetal_forces

^^ section 3 + 4

so for example, if you're rotating, you will feel a force keeping you from raising or lowering your arms, just like an ice-skater does when they're spinning, whether their eyes are open or closed.

does that sound right? i think that's right.

Interesting.

i bet caek would have a good understanding of this

Right, we should defer to the professional. Your argument seems valid though. Seems that if you are part of some rotating system and it is going fast and you are near the center you will feel it.

OK, you would probably feel it far out too, if you were rotating fast and there was kind of force other than, say gravity, holding you in place.

In orbit, rather.

This past summer at one point I had physics book on vacation and was going to try to think about conservation of angular momentum and how it usually has something to do with that ideal object of physics, the rigid body.

That wikipedia page is good. "Mach's principle" is a better formulation of the problem I was thinking of.

I agree now that you'd be able to feel it. Why this works under relativity is something I'll mull over.

Special or General?

I mean does relativity have anything to do with it? Special relativity deals with Galilean transformations at high speeds, inertial reference frames moving at constant (high) velocities away from each other, General Relativity treats of things being accelerated by (gravitational) forces. Rotating, non-inertial frames were studied well before a certain Swiss-German patent clerk came on the scene.

/subject_to_correction_by_caek

I mean obviously GR has to ultimately take into account rotation but not always vice versa.

Okay, found a good quote I may post later.

Or you could just google: Chandrasekhar "the subject quietly went into a coma."

I just meant without absolute space. I'm not well versed in this stuff (obviously?).

Sorry. I was wondering. In the beginning I was confusing you with ilxor alimosina, who does know about these things.

Maybe this will help a little, dunno: http://en.wikipedia.org/wiki/Angular_momentum

Okay, you wanted relativity so: http://www.einstein-online.info/spotlights/angular_momentum

Why this works under relativity is something I'll mull over.

A spinning body isn't an inertial frame of reference. There's no requirement, under the Galilean invariance which is the fundamental postulate behind both Special and General Relativity, for the occupant of a spinning closed room to be unaware of the rotation.

^^^

Aha. That makes sense.

I had done angular momentum in high school but needed a refresher.