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The Physics of a Rolling Rubber Band

CmdrTaco posted more than 4 years ago | from the thank-god-that-is-solved dept.

Science 226

sciencehabit writes "Modern physics can get complicated. Sure, researchers know exactly what forces act on a ball rolling down an incline — an experiment that helped Galileo develop universal laws for movement and acceleration. But what happens when a deformable shape like a rubber band rolls around? A new study reveals that the faster it goes, the more squashed it gets (video included)."

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Physics... (3, Insightful)

Pojut (1027544) | more than 4 years ago | (#33067626)

...is mind-boggingly awesome. I can't understand the math at all, but I understand the way things generally act. So cool (and so insanely complicated! Think about something like a key being inserted into a lock...and that's just simple, everyday stuff!)

Re:Physics... (4, Interesting)

SpinningCone (1278698) | more than 4 years ago | (#33067736)

i agree. I always liked physics made the world look different (like "car breaks are kinetic to thermal energy converters"). never could really get into dynamics though. i remember my teacher describing the the problem of rotational inertia of a deformable object (like a jelly disk) faster you spin the more it changes shape which changes its inertia.

props to the people out there with the knack and persistence to solve crap like that.

Brakes, please. Please? (4, Informative)

Kupfernigk (1190345) | more than 4 years ago | (#33067824)

I'm sorry but this is such a common mis-spelling on Slashdot that it's getting to me. Cars have brakes. "Car breaks" means it stops working because of mechanical or electrical failure. Spellcheckers can't fix homophones.

Re:Brakes, please. Please? (4, Funny)

Anonymous Coward | more than 4 years ago | (#33067860)

Spellcheckers can't fix homophones.

I can tell you have your spellchecker on, though I think you ment to write "homophobes".

I too believe they should be fixed.

LOL (0)

Anonymous Coward | more than 4 years ago | (#33067930)

Fascist.

Re:Brakes, please. Please? (0)

Anonymous Coward | more than 4 years ago | (#33067928)

But what if he drives it into something? You're definitely breaking the car, and applying the breaks at the same time. Unless you're one of those Toyota "drivers", then braking definitely doesn't apply.

Re:Brakes, please. Please? (3, Funny)

Bromskloss (750445) | more than 4 years ago | (#33068276)

Cars have brakes. "Car breaks" means it stops working because of mechanical or electrical failure.

I honestly thought he was talking about car crashes and even though that was a strange way of saying it, I convinced myselft that is was physically sound.

Re:Brakes, please. Please? (0)

Anonymous Coward | more than 4 years ago | (#33068306)

I'm right with you, but I think it's time to tie my t-shirt to a stick. I have a picture of a Mercedes TV commercial from BBC America, which has bold white type saying 'AUTOMATIC EMERGENCY BREAKING' right across the screen.

If Mercedes can't get it right, we may as well give up on Slashdot.

Re:Brakes, please. Please? (1)

ledow (319597) | more than 4 years ago | (#33068578)

While we're at it, can someone please bring up the following:

to/too/two
there/they're/their
your/you're
whose/who's

God, I know I'm pedantic but how hard is it to get *simple* things like this right? At least most of the time.
It severely hinders my reading speed if some text has simple mistakes like that. My mind jars as it hits them and slows me down.

Re:Brakes, please. Please? (2, Funny)

Anonymous Coward | more than 4 years ago | (#33068932)

Tell that to two Slashdot users whose who's are wrong too. They're messing up their you'res while your there's are perfect.

Re:Brakes, please. Please? (1)

allusionist (983106) | more than 4 years ago | (#33070098)

You mean "whose whos" not "whose who's" and "your theres" not "your there's." Stop abusing the poor apostrophe by needlessly jamming it into plural nouns.

Re:Brakes, please. Please? (1)

Guignol (159087) | more than 4 years ago | (#33069024)

Thank's I would of right it so my self but you bit me to eat.
I guess its fine I should of been more fasterer

Re:Brakes, please. Please? (0, Troll)

simcop2387 (703011) | more than 4 years ago | (#33069060)

don't forget about the other three!

you/yew/ewe!

Re:Brakes, please. Please? (1)

Guysmiley777 (880063) | more than 4 years ago | (#33069194)

How about "begs the question" used as "raises the question"? I know it's a lost cause but it still causes my eye to twitch.

Re:Brakes, please. Please? (1)

egomaniac (105476) | more than 4 years ago | (#33069436)

I think you're on the wrong side of this one, obviously. Words and expressions change meaning over time, and at this point you might as well be upset over the fact that people use the word "computer" to mean "electronic calculating device" instead of its original meaning, "a person who performs tedious calculations by hand".

It's time to give up and accept that you have lost the fight. "Begs the question" now means "raises the question".

Re:Brakes, please. Please? (1)

quadrox (1174915) | more than 4 years ago | (#33069974)

Even worse, my mind has started to "crash" on rare occasions when people write "could have" instead of "could of" and similar stuff, simply because it is so rare to see it spelled right nowadays. That's really messed up.

Re:Brakes, please. Please? (0)

Anonymous Coward | more than 4 years ago | (#33069086)

There is no hyphen in the word "misspelling."

Re:Brakes, please. Please? (1)

clone53421 (1310749) | more than 4 years ago | (#33069236)

There can be [merriam-webster.com] .

Re:Brakes, please. Please? (0)

Anonymous Coward | more than 4 years ago | (#33069334)

Miss Pelling was recently wedded to Mr. Don T. Grammer.

Re:Brakes, please. Please? (1)

Twinbee (767046) | more than 4 years ago | (#33069392)

I was going to moan at you that it was obvious from the context that he meant 'brakes', but then someone goes and replies to you and thought he really did mean 'break'. Sigh... I was really going to enjoy the moan too ;)

Re:Brakes, please. Please? (3, Funny)

boxwood (1742976) | more than 4 years ago | (#33070196)

a bit of tape stuck over the bottom left corner can fix a homophone.

Re:Physics... (0)

Anonymous Coward | more than 4 years ago | (#33069620)

those problems you are talking about are called "differential equations", and guess what, you couldnt get into them because they are in fact, fucking heavy shit, and most often not even analytically solvable. that jelly disk though, is. assuming linear deformation. id recommend you to start reading into the harmonic oscillator if you want to dig into diff equations.

Re:Physics... (4, Funny)

Anonymusing (1450747) | more than 4 years ago | (#33067742)

Physics is pretty cool.

I liked this quote from the article:

As far as the potential applications, Clanet waxes futuristic. "I can imagine [designing] a car. The faster it goes, the more it deforms and the less friction it has with surrounding air, so it can go even faster. It would be a fantastic car."

A car that changes its shape as it drives? Getting shorter, even? "Ouch, slow down, you hit my head!"

Automobile safety experts would have a field day with that.

Re:Physics... (1)

snookerhog (1835110) | more than 4 years ago | (#33067812)

the vehicles changing shape comment reminds me of the SR71. Only when it gets up to speed do the joints close up and the skin smooth out due to air friction heating it up. The think leaked fuel like a sieve on the tarmac apparently, but was tight as a frog's ass at mach 3.

Re:Physics... (3, Funny)

VolciMaster (821873) | more than 4 years ago | (#33068262)

I love Ben Rich's quote on that: "no one's been wing-walking at Mach 3 to verify that assumption" :)

Re:Physics... (1)

zaaj (678276) | more than 4 years ago | (#33067842)

Yeah, that quote bothered me too - I'm thinking, why not just design it with the least friction with the air to start with - why have it be less efficient at slow speeds in other words?

Unless Clanet was referring to the design process itself - use an elastic model in a wind tunnel (or simulate the whole thing) and observe it's deformation to determine the shape with the least friction with the air (or call it coefficient of drag, like everyone else does :-)

At first I was thinking it might have been typical media-distorted science, but when they threw in that quote from Clanet, it seemed more that the science is hard to take seriously too.

Re:Physics... (3, Insightful)

EdZ (755139) | more than 4 years ago | (#33068050)

Because air behaves differently at different speeds. Once you got fast enough, shockwaves become the limiting factor rather than fluid fraction. Then you have cavitation, and things like compression heating. What is most efficient at one speed is not most efficient at all speeds.

Re:Physics... (1)

Twinbee (767046) | more than 4 years ago | (#33069482)

That sounds interesting. Can you give the associated speeds that those things separate phenomena start to occur at?

Re:Physics... (2, Insightful)

VolciMaster (821873) | more than 4 years ago | (#33068344)

Yeah, that quote bothered me too - I'm thinking, why not just design it with the least friction with the air to start with - why have it be less efficient at slow speeds in other words?

Unless Clanet was referring to the design process itself - use an elastic model in a wind tunnel (or simulate the whole thing) and observe it's deformation to determine the shape with the least friction with the air (or call it coefficient of drag, like everyone else does :-)

At first I was thinking it might have been typical media-distorted science, but when they threw in that quote from Clanet, it seemed more that the science is hard to take seriously too.

Just a quick thought, but at low speeds aerodynamic efficiency is of very low impact (eg a barge at 2 kts and a kayak at 2 kts). The faster they go, the more that efficiency matters - having a material that could deform to improve flow as speeds increased could be a good thing - especially if it were used around the freight compartments of a tractor-trailer or rail car: squishing-down to more evenly flow around the carried contents could have some promise.

Re:Physics... (1)

AndersOSU (873247) | more than 4 years ago | (#33069232)

It gets even more interesting than that. There's two main types of drag, friction drag and pressure drag. Friction drag is generated from air molecules slamming into the object and the fact that very close to the surface of the object the fluid is slowed (known as the no-slip condition). Pressure drag is a bit less intuitive, but it's what makes drafting work in both nascar and cycling. As you speed up an area of low pressure develops behind you as the flow separates at the back of the object. This low pressure literally sucks you backwards. Finally there is a discontinuity in drag at mach 1 when shock waves and the like develop.

At low speeds friction drag tends to dominate and this drag can be reduced by improving the aerodynamics of the leading edge of the object. At high speeds pressure drag tends to dominate and this can be reduced by modifying the trailing end of the object - which why time-trial racing bike helmets are pointed at the back. The other thing you can do is add texture which separates the flow from the object and usually reduces the size of the low pressure bubble behind it, and this is why golf balls are stippled.

One last interesting bit. The angle the shockwave of a supersonic object takes is a function of speed, not shape. If you're a plane designer you want the largest wing area as possible within that shock wave (things projecting into the shock have a nasty tenancy to be ripped off.) So while the top speed of the SR-71 is still technically classified (or at least it was when I took fluid dynamics), by measuring the angle from the nose to the wingtips you can calculate the top design speed remarkably easily.

Re:Physics... (2, Interesting)

Seismologist (617169) | more than 4 years ago | (#33067902)

...is mind-boggingly awesome.

Actually you can often make a simple assumption and work off of F = m*a or some other well established theorem...

As for the math, now that is some pretty mind boggling stuff. Some of the math that was used to pull string theory together is pretty bleeding edge on top of the physics part of it. PBS had a interesting show on string theory(you can watch in three installments on PBS [pbs.org] ). What struck me the most was how splintered the physics community was as many researches were doing the math a certain way different from each other, but it was found to be all the same by another physics/math guru when he proposed 11 dimensions instead of 9 like the other researches had inferred.

Re:Physics... (0, Troll)

GNUALMAFUERTE (697061) | more than 4 years ago | (#33067986)

Oh, if you don't understand the math at all, then you are totally qualified to write articles for sciencemag.org.

Here is how it basically works:

1) You made some dull experiment, very simple setup, that leads nowhere, and allows no data collection at all.
2) Write down "Woah, awesome, if were like it would be, like, great, amirite?
3) Publish.
4) ???
5) Get to the frontpage of /.

The article reminded me of this: http://xkcd.com/171/ [xkcd.com]

Re:Physics... (0)

Anonymous Coward | more than 4 years ago | (#33068150)

best xkcd ever!

Re:Physics... (0)

Anonymous Coward | more than 4 years ago | (#33068520)

Fucking keys, how do they work?

Re:Physics... (0)

Anonymous Coward | more than 4 years ago | (#33068844)

so you're saying if i roll a peanut down an incline that it'll make peanut butter if it goes fast enough?
is this peanut butter going to be spread down the incline or is it going to be at the very end, where the incline hits a giant BRICK WALL? :)

Every time you roll a rubber band... (0, Offtopic)

Luke727 (547923) | more than 4 years ago | (#33067632)

...a nigger dies.

Delight to read... (2, Funny)

ZeroExistenZ (721849) | more than 4 years ago | (#33067662)

But what happens when a deformable shape like a rubber band rolls around?

... the article sounds like the things I used to wonder about and do during boring classes in highschool.

Re:Delight to read... (2, Funny)

jamesh (87723) | more than 4 years ago | (#33067720)

... the article sounds like the things I used to wonder about and do during boring classes in highschool.

Same here, except I was more like "I wonder if I can hit that kids sticking-out ears with a rubber band from here", without thinking through what would happen if i _did_ hit them (which should have been obvious in retrospect... it was for that reason I sat at the back).

Re:Delight to read... (1)

VolciMaster (821873) | more than 4 years ago | (#33068356)

... the article sounds like the things I used to wonder about and do during boring classes in highschool.

Same here, except I was more like "I wonder if I can hit that kids sticking-out ears with a rubber band from here", without thinking through what would happen if i _did_ hit them (which should have been obvious in retrospect... it was for that reason I sat at the back).

..guess it depends on how big the kid with the sticking-out ears was, eh?

Re:Delight to read... (2, Funny)

Scatterplot (1031778) | more than 4 years ago | (#33068566)

No, it depends on how fast he was rolling. I think.

Re:Delight to read... (1)

PitaBred (632671) | more than 4 years ago | (#33069698)

If you want to make sure you do hit the ear, make one "side" of the rubber band tighter than the other when you shoot it. It makes it spin in flight and stabilizes it's trajectory. I can nail a fly from 10' with the right technique ;)

Re:Delight to read... (4, Funny)

Spad (470073) | more than 4 years ago | (#33067856)

I like to imagine that all scientists operate on this principle. They sit around doing boring paperwork until one of them says "I wonder what happens when a deformable shape like a rubber band rolls around?", to which one of the others replies "Quickly, to the lab!" and they all run off to investigate it.

Re:Delight to read... (1)

gl4ss (559668) | more than 4 years ago | (#33067958)

if it's worth publishing, I'd have hoped for it to be worth to them to have an incline to roll it down on, instead of having it in a rolling drum. like, get out of the damn room if it's too small. now i'm just left wondering if it spun along with the drum and got squashed because of that.

Re:Delight to read... (1)

VolciMaster (821873) | more than 4 years ago | (#33068374)

if it's worth publishing, I'd have hoped for it to be worth to them to have an incline to roll it down on, instead of having it in a rolling drum. like, get out of the damn room if it's too small. now i'm just left wondering if it spun along with the drum and got squashed because of that.

maybe they used a drum because setting-up a camera along a 50 foot ramp would've been cost-, space-, or effort-prohibitive?

Indeed (1)

stomv (80392) | more than 4 years ago | (#33069750)

but I'm surprised that they didn't get a bigger drum, in order to minimize the curvature of the surface with which the elastic was in contact. I have no idea if their model corrects for the fact that the elastic is not rolling down a 'flat' surface, but rather one with a curve. Bigger drum, smaller curve.

Wow, interesting! (4, Interesting)

rotide (1015173) | more than 4 years ago | (#33067722)

If you would have asked me how it would react as it rolled faster and faster, I would have just assumed it would have gotten "rounder" and possibly larger (elastic) due to centrifugal force.

Always amazes me how things don't always work as expected. Nature, physics, etc, are truly interesting... no, fascinating. Now if only I had a better grasp of higher level maths and wasn't a Network Engineer (data plumber).

Re:Wow, interesting! (0)

Anonymous Coward | more than 4 years ago | (#33067756)

[theatrical voice] "na-TUUUUUREEEE is AWE!! SOME!!!!"

Re:Wow, interesting! (1)

V!NCENT (1105021) | more than 4 years ago | (#33067768)

"I would have just assumed it would have gotten "rounder" and possibly larger (elastic) due to centrifugal force"
It does get round and evens out, but due to gravity the evened out band gets pulled down and the resistans on the 'outward ends' all result on a peanut form.

Geez that was mind-bloooooowwwwwiiiiiing.......

So how's the LHC doing?

Re:Wow, interesting! (0)

Anonymous Coward | more than 4 years ago | (#33069530)

It's still long and hard...

Re:Wow, interesting! (3, Funny)

Spad (470073) | more than 4 years ago | (#33067874)

...due to centrifugal force.

My high school physics teacher used to electrocute (With a handheld generator made from a rotary pencil sharpener) people for saying that; also for misspelling accelerate or satellite.

Re:Wow, interesting! (1)

Yetihehe (971185) | more than 4 years ago | (#33067974)

Obligatory xkcd link: http://www.xkcd.org/123/ [xkcd.org]

Re:Wow, interesting! (1, Interesting)

silentcoder (1241496) | more than 4 years ago | (#33068028)

>>...due to centrifugal force.

>My high school physics teacher used to electrocute (With a handheld generator made from a rotary pencil sharpener) people for saying that; also for misspelling accelerate or satellite.

Yes a common reaction of overzealous highschool teachers - and wrong. Do the math. Forces per se is an oversimplification as it is, useful to model certain aspects of physics, and not for others. Gravitons attract one another, thus is created what we PERCEIVE as the force of gravity if you go down to the quantum level for example.

At the level of Newtonian physics - centrifugal force is as real a force effect as any of the others. True it's a consequence of other forces working together and against each other but it's there nonetheless and it's impact is crucial to predicting how many things will behave.
When two forces work at an angle - the object moves along a (predictable) path created by both forces - it is both correct and useful to model that path as a force in it's own right. At least it OFTEN is, always remember that no scientific model is ideal for EVERY scenario - that's why we don't just HAVE one scientific model.
You want to know how gas will fill a chamber - gravity has so little influence that it's not worth thinking about, quantum mechanics is your friend there. You want to know how it will fill a universe - gravity becomes very important suddenly and this is why the universe does not have it's gases distributed as quantum mechanics would predict, instead of entropy, the universe got decidedly clumpier over time.

For some problems - it's incredibly useful to model centrifugal effects as a force, for others it's much more crucial to work on the shaping forces that create it in the first place - but it's not "wrong" to talk about a centrifugal force if what you want to describe is the effect it causes.

Re:Wow, interesting! (1)

silentcoder (1241496) | more than 4 years ago | (#33068164)

Also XKCD agrees with me which renders any arguments invalid.

Re:Wow, interesting! (1)

Guignol (159087) | more than 4 years ago | (#33069872)

The overzalots teachers are right and misquoted.
When they say 'there is no centrifugal force but instead a centripetal force' they don't say it our of nowhere at any time just to hurt your feelings
Whenever a child get in school starting to learn basic physics, he almost always 'know' about the so called 'centrifugal force' meaning the force you experience when you are in a rotating wheel, orthe force that will prevent the water from falling in a fast rotating bucket attached to a rope (etc.)
So the teacher will rightly say that the observed effect is not due to any centrifugal force, and indeed it could not be modelled so, the only 'force' is centripetal (right of course it has its reaction) but what the children 'feel' and attribute to a centrifugal force is in fact inertia which by the way is not centrifugal since as soon as the centripetal force will cease the inertia will lend the mobile to follow a tangential trajectory
Of course you can still confront magnets or electrical charges to show that there are indeed such things as centrifugal forces but it has nothing to do with the 'evil stupid teachers' arguments when they want to make a point about the centripetal vs centrifugal force

Re:Wow, interesting! (0)

Anonymous Coward | more than 4 years ago | (#33068288)

My high school physics teacher used to electrocute people for saying that

Killing students seems a bit excessive! Or did you just mean he gave them an electric shock?

Re:Wow, interesting! (1)

VolciMaster (821873) | more than 4 years ago | (#33068384)

...due to centrifugal force.

My high school physics teacher used to electrocute (With a handheld generator made from a rotary pencil sharpener) people for saying that; also for misspelling accelerate or satellite.

ah yes... "centrifgual force" - that force applied by a centrifuge.

Re:Wow, interesting! (4, Interesting)

ledow (319597) | more than 4 years ago | (#33068478)

Yes, but then people "weigh" themselves in kg's by standing on a scale that is affected by gravity.

There are certain things that, although "visible" by ordinary people and named, don't actually exist or exist only because we *perceive* them to exist, like that optical illusion with the white triangle that isn't ACTUALLY there.

Centrifugal force may be misnamed (i.e. not a force), it may be incorrect, but it's generally accepted that "a force" exists that has an effect on your when you're spun in a circle. Just because the direction / origin / name of that force is incorrect is no reason to tell people that they're stupid for having felt it and knowing what it is before you explain its origins.

Back in the 60's there was an advertising campaign by scientists working on the behalf of government to target heat loss in elderly people's properties. It encouraged old people to "keep the heat in". It didn't go down well and it took them years to discover why. Eventually it was changed to "keep the cold out" and more elderly people understood that. "Cold" doesn't actually exist, it's just the absence of heat, but old people didn't think that way as easily (and who can blame them? "Shut the door, you're letting the cold in" is a common cry in my family - despite the fact that you're neither letting cold in nor arranging for some mystical "cold" entity to enter your property rather than, say, air with slightly less heat).

There's 100% pedantic accuracy. There's complete bollocks. And somewhere in the middle is how *everybody* thinks, even if they know both extremes in detail.

Re:Wow, interesting! (1)

Twinbee (767046) | more than 4 years ago | (#33069638)

Even on a pedantic level though, it's correct to say something's colder *relative* to something else, rather than as an absolute level of cold. Also bear in mind that they're talking about the sensation/feeling of cold rather than its physical makeup. On a certain level, red is best spoken about by its name rather than its wavelength. It's just a different kind of pedantic-ness, not necessarily less pedantic.

Re:Wow, interesting! (1)

clone53421 (1310749) | more than 4 years ago | (#33068032)

Spinning faster = more velocity perpendicular to slope on the leading edge of the loop. It makes sense that it would flatten out.

Re:Wow, interesting! (1)

XSpud (801834) | more than 4 years ago | (#33068038)

If you would have asked me how it would react as it rolled faster and faster, I would have just assumed it would have gotten "rounder" and possibly larger (elastic) due to centrifugal force.

And I'd think for a suitably low coefficient of friction between the band and the ground you'd have been right.

Re:Wow, interesting! (1)

Seismologist (617169) | more than 4 years ago | (#33068790)

Network Engineer (data plumber)

I never understood the whole "engineer" term being attached to everything in IT anyway such as network engineer. I used to work in a role as what can be described nowadays as a "network engineer", but I don't see any of the virtues of engineering applied to this occupation.

Engineering is a profession (a profession in the sense of being a lawyer, doctor, etc. with certification behind it -- as opposed to an occupation such as a plumber) that uses and applies the knowledge of basic engineering principals and math to address practical issues that may have direct consequences to property and the public. Data networking is more of a business problem sort of philosophy.

Now maybe if you were to design a layout of conduits and had to calculate power usage used by equipment, breaker panels, and other things of that nature for a system/installation (such as at a data center), I would certainly consider this to be engineering, and you would most likely be required to apply your PE (professional engineer) stamp as an “electrical engineer” to the design and drawings of said system and NOT as a “network engineer”. I don’t foresee a stamp being used by a “network engineer” unless that engineer happens to be a registered “Professional electrical Engineer”.

Also, be aware that using “engineer” in your title, while not being a certified as engineer (as defined by your State/Provincial department of licensing) is just as misleading as saying you’re a network doctor, or network lawyer. The title PE, or Professional Engineer, is a registered trademark in the US.

The term “engineer” in any title in Canada is regarded as a trademark. This got Microsoft into trouble in Canada [slashdot.org] when they were offering “MS engineering certificates”. There is a Wikipedia entry (en.wikipedia.org/wiki/Controversies_over_the_term_Engineer [slashdot.org] ) about this all this as well well.

Now network researcher, network scientist, network analyst, these are all more appropriate title to the occupation.

Re:Wow, interesting! (1)

rotide (1015173) | more than 4 years ago | (#33069064)

Contact my boss and HR to have my title changed to meet your, apparently, delicate sensibilities. Either that, or get off your high horse and stop complaining about arbitrary job titles that change at the mere whim of the aforementioned persons.

Or, to put it another way, stop being so damn pedantic. I've honestly never seen a rant so serious about something so meaningless.

Re:Wow, interesting! (1)

FrigBot (1459361) | more than 4 years ago | (#33070182)

In Canada we take this especially seriously, and our provincial associations will go so far as to take a usurper of the term "engineer" to court to require them to change their title. The bottom line is that the public is meant to know that they can trust the professionalism and competency of a real engineer. You count on us to design things which will be safe. And to claim you are an engineer (network, petroleum transfer, etc.) is misleading to the public in the sense that you understand the ramifications of that public trust in doing your work. It's not meaningless.

And to the hoser below, regarding train engineers (drivers), they are specially exempted because it is a time-honoured tradition for them to be called engineers, and everyone knows what it means, so there's no problem there. Thus we can call them engineers, and we all know that it doesn't mean quite the same thing as a professional engineer. Unless they have an engineering degree.

Re:Wow, interesting! (0)

Anonymous Coward | more than 4 years ago | (#33069442)

What do you call the person who drives a train?

model (0)

Anonymous Coward | more than 4 years ago | (#33067848)

>> researchers know exactly what forces act on a ball rolling down an incline

No they dont, they just think they have a good working model.

How do you make it interesting to students (1)

dimethylxanthine (946092) | more than 4 years ago | (#33067884)

Rolling rubber band, Faster!, squashed, ball, acceleration... Finally, some sex in the realm of physics! If only my physics (and math!) books had this many innuendos on one page...

centrifugal forces (1)

StripedCow (776465) | more than 4 years ago | (#33067890)

However, if the rubber band is spinning really fast, aren't the centrifugal forces pushing the band outward, compensating the squashing?

Disclaimer: I didn't RTFA.

Re:centrifugal forces (1)

talz13 (884474) | more than 4 years ago | (#33068016)

It's the centripetal forces that are pulling the band towards the center, there is no force pushing the band outwards (the band really just wants to keep going in a straight line, but can't due to the force pulling it inwards). It is easier to illustrate with the weight being swung in a circle attached to the end of a string, where the string is providing the inward force.

Re:centrifugal forces (1)

StripedCow (776465) | more than 4 years ago | (#33068144)

Yes, of course the centripetal force is the opposite of the (fictitious) centrifugal force in Newton's third law.

Re:centrifugal forces (1)

clone53421 (1310749) | more than 4 years ago | (#33068082)

Centrifugal force doesn’t exist. It is simply our perception of momentum in a spinning object.

Re:centrifugal forces (1)

StripedCow (776465) | more than 4 years ago | (#33068176)

Forces do not exist. They are simply our perception and our way of modeling certain aspects in nature. Centrifigal forces are simply a way of referring to the opposite of centripetal forces (in Newton's third law).

But that was entirely not the point.

Re:centrifugal forces (1)

clone53421 (1310749) | more than 4 years ago | (#33068298)

So what you are saying is, centrifugal force is the equal and opposite force to the force you must apply to move a rotating system’s centre of mass.

No... that’s simply its momentum. Or its inertia, as they are the same thing.

Re:centrifugal forces (1)

Culture20 (968837) | more than 4 years ago | (#33068106)

However, if the rubber band is spinning really fast, aren't the centrifugal forces pushing the band outward, compensating the squashing?

You also didn't read your physics book. There is no such thing as centrifugal force (outward from center).

Re:centrifugal forces (-1, Redundant)

Anonymous Coward | more than 4 years ago | (#33068192)

http://xkcd.com/123/

Re:centrifugal forces (1)

flaco629 (1671226) | more than 4 years ago | (#33068248)

Centrifugal forces don't exist. They are fictional forces used to make non-inertial frames of reference conform to Newton's laws. So they aren't going to compensate for much of anything.

BZZT! WRONG! (2, Interesting)

gbutler69 (910166) | more than 4 years ago | (#33069356)

You, like many of the others above, FAIL! There is Centrifugal Force. If I spin a rock at the end of a rope, the rock experiences a "Centripetal Force" which is a force pulling towards the center of a circle, where my hand is, that is perpendicular to it instantaneous velocity. Note, it is not only experiencing a "Centripetal Force", otherwise it would just accelerate along the radius toward the center. It is in fact also experiencing a force along the tangent (i.e. the diretion of instantaneous velocity) of the same circle. But, here is where it gets interesting. It is actually experiencing neither of those. It is in fact experiencing a force that is at an angle slightly between the direction of the tangent to the circle and along the radius. We can break that actual force (the real direction I'm actually pulling on the string) into the component along the radius and the component along the tangent, but, there really isn't two separate forces acting, just one. So, what you are calling "Centripetal Force" doesn't actually exist either. It's just a a convenient name for the component of the force pulling inward along the radius. Now, according to Newton's Laws, for every force (action) there is an equal an opposite force (re-action). So, if there is a corresponding force pulling inward on the rock (the "Centripetal Force") then there is also a force pulling outward along the radius (the "Centrifugal Force"). In fact, the Rock is pulling on my hand with such an equal and opposite force. So, my hand (and the string) is experiencing "Centrifugal Force". So, "Centrifugal Force DO EXIST!" You FAIL! Go back and re-read your Physics text-book and try again!

Thank You for Playing!

Oh, one other thing... (1)

gbutler69 (910166) | more than 4 years ago | (#33069438)

Every Molecule in the Rock and String, other than the single Molecule that is farthest from the center of the circle, simultaneously feels a Centripetal, and Centrifugal Force. That is because that while each molecule is experiencing a force pulling towards the center of the circle, that same molecule is also pulling on the next molecule in the chain, which is pulling back, therefore the first molecule experiences a "Centrifugal Force" equal to the "Centripetal Force" it pulls with to the next molecule in the chain. So, one can say everything in the system other than the outermost molecule is experiencing "Centrifugal Force". Now, is it so incorrect to talk about "Centrifugal Force"? Me thinks not. It is simpler to think of the system in terms of "Centripetal Force" and "Radial Force", but, you can also think of it in terms of "Centrifugal Force" quite well.

Re:BZZT! WRONG! (1)

flaco629 (1671226) | more than 4 years ago | (#33069926)

You certainly are abrasive, for being so wrong. I read physics books every day, since I am a physicist.

Re:BZZT! WRONG! (1)

clone53421 (1310749) | more than 4 years ago | (#33070050)

What you mean is, this is a REAL imaginary force that you invented to FIX Newton’s INCORRECT laws of motion so that they can apply to situations that they DON’T APPLY TO.

http://en.wikipedia.org/wiki/Newton's_laws_of_motion [wikipedia.org]

Newton's Laws hold only with respect to a certain set of frames of reference called Newtonian or inertial reference frames.

Fail, indeed...

Direct link to the .FLV (3, Informative)

Anonymous Coward | more than 4 years ago | (#33067914)

For those of us where the player won't launch when you click "play video" in the article, here's a direct link to the flash video:

http://sciencevideo.aaas.org/sciencenow/snow_ribbon_250.flv [aaas.org] (320x240, 17 seconds, 1.1MB)

Re:Direct link to the .FLV (1)

dborod (26190) | more than 4 years ago | (#33070184)

Thanks. I wonder why the video wouldn't play for me on the site?

This requires a government study (1)

countertrolling (1585477) | more than 4 years ago | (#33067954)

Similar to the one done to determine the flow rate of ketchup...

Re:This requires a government study (0)

Anonymous Coward | more than 4 years ago | (#33068076)

yea I know, its basic high school science, and we paid researchers to tell us that?

9th grade science 101 has centripetal force in it

This requires Yakety Sax (5, Funny)

cangrande (199946) | more than 4 years ago | (#33068140)

All science videos are improved by Yakety Sax.

Miracle (5, Funny)

JustOK (667959) | more than 4 years ago | (#33068182)

Fucking rubber bands, how do they work?

Re:Miracle (1)

TapeCutter (624760) | more than 4 years ago | (#33069394)

"Fucking rubber bands, how do they work?

Feynman to the rescue [youtube.com] .

The phenomena in TFA is just begging for a numerical simulation. I wonder if something like Blender or PhysX would predict this behaviour correctly?

Makes perfect sense. (1)

clone53421 (1310749) | more than 4 years ago | (#33068218)

It’s all about the deformability of the loop. In a perfectly circular loop, the intersection with the ground is tangential. If the loop deforms, it strikes the ground rather than intersecting tangentially, and the faster it spins, the harder it hits the ground. The harder it hits, the more it deforms.

Alternately, as I see it, if it is accelerating due to its friction with the ground (i.e. if you spin it up first and then let it go) it should be able to temporarily keep itself supported under its own momentum, but as soon as that friction drops to zero it will begin to collapse due to its own weight and then the above will apply. As long as the frictional force vector is zero or points backward, the band should deform. Naturally I’ll be needing a few hundred thousand dollars to be testing my theory.

Re:Makes perfect sense. (1)

pz (113803) | more than 4 years ago | (#33068592)

It’s all about the deformability of the loop. In a perfectly circular loop, the intersection with the ground is tangential. If the loop deforms, it strikes the ground rather than intersecting tangentially, and the faster it spins, the harder it hits the ground. The harder it hits, the more it deforms.

Alternately, as I see it, if it is accelerating due to its friction with the ground (i.e. if you spin it up first and then let it go) it should be able to temporarily keep itself supported under its own momentum, but as soon as that friction drops to zero it will begin to collapse due to its own weight and then the above will apply. As long as the frictional force vector is zero or points backward, the band should deform. Naturally I’ll be needing a few hundred thousand dollars to be testing my theory.

Just watch a little top fuel drag racing to see tire (a/k/a elastic loop) deformation under load.

Re:Makes perfect sense. (1)

clone53421 (1310749) | more than 4 years ago | (#33068664)

One could do that; however I do not think they are a very good subject to study this effect. They are moving too quickly to observe very well without high-speed camera equipment, heavily loaded (apart from their own weight), and designed to deform as little as possible under smooth conditions because tire deformation increases the drag on the vehicle (remember that over-inflating your tires will increase your gas mileage?).

Is this valid, spinning inside another wheel? (1)

guidryp (702488) | more than 4 years ago | (#33068402)

Won't there be Centrifugal/Centripetal forces from the drive wheel it is running inside?

Or do these forces not exist because the rubber band is essentially stable in it's position inside the wheel?

Re:Is this valid, spinning inside another wheel? (1)

minogully (1855264) | more than 4 years ago | (#33068540)

Yeah, the first thing I thought when I saw this, is, the surface that the rubber band is rolling on is curved inwards! I thought they were studying the movement of it rolling down a hill... I wonder if there are any significant differences between the behaviour of this experiment vs. the behaviour of a rubber band rolling along a tilted conveyor belt? What about a surface curved in the other direction?

Re:Is this valid, spinning inside another wheel? (0)

Anonymous Coward | more than 4 years ago | (#33069320)

I thought the same thing, I think this is an extremely flawed experiment which proves nothing. The centripetal force of the hamster wheel on steroids is simply forcing the middle of the rubber band towards the wall of the wheel and the edges have more structure to resist the force. I was intrigued until I saw the video, completely worthless.

Re:Is this valid, spinning inside another wheel? (1)

Scatterplot (1031778) | more than 4 years ago | (#33068726)

As some of the other posters have said, since "centrifugal" forces "technically don't exist" then no. What is perceived as centrifugal force is really the momentum of an object being acted on by the rotating vessel (in this case it would be the wall of the container). So while the rim experiences forces that look like forces pulling it to the center, the rubber band would not, since it's not rotating. However, the rubber band *itself* is rotating, so internally there would be "centrifugal" forces, which is where the peanut shape comes from.

Isn't the center of a golf ball a rubberband ball? (1)

realsilly (186931) | more than 4 years ago | (#33068476)

Ok so if I remember correctly, the center of a golf ball is made with a rubberband like substance, and then is covered with that nice hard plastic shell. But as a golf ball lands and rolls, wouldn't that spin cause the same reaction as what is in that video? Or could we assume that it is so tightly wound and then encased with little to no wiggle room that this alteration of shape would not take place? I'm thinking it's the latter.

Next I'd love to see the same thing performed with the traditional egg drop experiment and how long the egg would last.

Re:Isn't the center of a golf ball a rubberband ba (1)

teebob21 (947095) | more than 4 years ago | (#33069216)

This.

it is so tightly wound and then encased with little to no wiggle room that this alteration of shape would not take place.

Why can't we model this? (1)

CrazeeCracker (641868) | more than 4 years ago | (#33068628)

Every time I hear of a story similar to this one, I'm reminded of something that has always puzzled me:

We are aware of all the (relevant) forces at work in and on the rubber band. At a sensible scale, for all intents and purposes, we could say we understand the rubber band perfectly. (Right?)
So the only thing holding us back from modelling this kind of stuff is computational resources, which, I would assume, should not be that much of a problem with today's supercomputers. (Right? I mean it doesn't have to be in real time.)
So why aren't we doing it? In Physics we deal with equations that involve approximations a lot of the time, but that's more out of convenience and simplicity than out of a lack of understanding of our world (again, at a scale where we can use classical physics).
Take thermodynamics. Or fluid dynamics. They're both just approximations of atoms interacting in a way that is very much understood already, but we keep them around because it's easier to imagine the physical implications of a concept like temperature or drag force, rather than millions upon millions of tiny particles bouncing around semi-randomly.

I guess my point is, if they can have virtual wind tunnels, why can't they have virtual rubber bands? As a matter of fact, why can't we calculate the properties and interactions of a significant fraction of the things around us without the need for experiment?

Flying out of the drum (3, Interesting)

azmodean+1 (1328653) | more than 4 years ago | (#33068670)

I was amused by this aside:

(The team couldn't study what happened when the two sides touched: The friction of the two sides moving in different directions sent the rubber bands flying out of the drum.)

What? It seems pretty obvious that they could see exactly what happened when the two sides touched, "The friction of the two sides moving in different directions sent the rubber bands flying out of the drum".

Pulling it together (0)

Anonymous Coward | more than 4 years ago | (#33068768)

Ummm... how much of a stretch was it to write/fund the research/report?

In other news (1)

hviniciusg (1481907) | more than 4 years ago | (#33069268)

"study reveals that the faster it goes, the more squashed it gets."

in other news, when it rains things get wet

Seems to be remembering the curvature of the drum (1)

spads (1095039) | more than 4 years ago | (#33069846)

The idea is that as they speed it up, it doesnt have time to "relax" from its curvature from conforming to the drum. They should try it with larger diameter drums.

So called "visco-elastic" materials (e.g. polymers) are extremely interesting. Basically, you can clearly see the (mechanical) molecular properties manifesting themselves at the mechanically at the macroscopic scale. If I am write about this one, that would be mainly due to the viscosity.
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