Flight of the Pole Dancer

Welcome to PopSci's newest blog feature, "The Breakdown." Each week, we'll pick a Web video that involves a minor crash, explosion or other nonfatal mishap and invite one of our experts to explain, in scientific terms, what went wrong. In this week's edition, physics whiz Michael Moyer analyzes the case of the tumbling pole dancer...

Newton’s First Law of Motion states that bodies in motion tend to stay in motion. The same holds true for rotating bodies and, as we see in this video, doubly true for rotating, gyrating bodies.

Consider the body of the body in question. After a quick shake of the head right and left, she leans backward to begin her rotation around the pole. Her pivot points include her right hand, held fast to the pole, and her left foot (disastrously clad, we will soon learn, in three-inch heels). She now has a sizeable amount of angular momentum moving counterclockwise around the pole, and this can be halted only by an external force.

Unfortunately for our young dancer, the outcropping of wall her rear end soon encounters does not provide that force. Instead it simply serves as a new fulcrum, shifting the center of rotation from her hand to her hip. This does two things: Like a figure skater pulling her arms in, shifting the center of rotation closer to her center of mass acts to speed the rotation up. More important, it also means that her right hand must begin to rotate around the wall as well.

The outcome is predictable. A hand rotating away from the pole cannot continue to hold onto the pole, and without that grip, our dancer loses her balance in a most sudden and undignified fashion. Lesson learned: Newton can still represent. Can you think of a YouTube video you'd like explained? Send us a link in the comments section. —Michael Moyer

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*The embedded video that used to live here was removed from YouTube because of copyright silliness. But you can still see it at Break.com*

Comments

[HumanGame]

One thing I would add, the probable influence of alcohol to our subjects lack of balance and it's aid to Newtons first law in this matter.

Keep the "Breakdowns" coming.

[Larian LeQuella]

Assuming her to be a petite young woman, what sort of strenth would she have to posses in her hand (and arm) to actually manage to hold on to the pole? Let's say she weighs 110 lbs?

[Tonik]

The figure skater reference is bullshit.

[Brit]

This is a great idea for a web series. Love it.

But she fell because of Murphy's First Law of Drinking... never drink so much that you lose your grip on the planet, or something like that.

[Wang Junyu]

Have a question. Why you said this event is like a figure skater pulling her arms in? In the video when the dancer changed her fulcrum, the velocity remained constant, not the angle momentum.

[Tarantulas]

"The figure skater reference is bullshit."

Great job backing up your statement! You should totally write for "No one cares what you think" magazine!

[Modern Polymath]

The video was funny. This, on the other hand... not so much.

[yatpay]

Great idea! I've often wondered what happened in a lot of online videos.

I'm pretty sure I know what happened here, but it still might be good to write about: http://www.youtube.com/watch?v=_uEyhEcZLG0

[Dondee]

Assuming her to be a petite young woman, what sort of strenth would she have to posses in her hand (and arm) to actually manage to hold on to the pole? Let's say she weighs 110 lbs?

Well if she was not as petite and had more mass and proportional arm strenght for her size, and afer observing the flexing of the pole and the shape of the pole, I would think she may have been able to pull the pole down with her.

[Anonymous]

Please explain this:
http://www.youtube.com/watch?v=S1HBuAduTo0

What the hell went wrong?

[Sccerfrk26]

This video is pretty cool:

http://youtube.com/watch?v=c3asSdngzLs

[rancid meat]

Physics is science, but the wrong science is being applied to this video. If you watch the video, you see she looks at the wall, just before she makes the exptended pose. Also she but her hand behind her, feeling for the wall. This leads me to believe she was fully aware of the wall. What she did not account for, was the step! Her foot, althought not seen in the video at the time, clearly steps, at least partialy, over the edge. This is why she falls and not because of, "a new fulcrum". Therefore we are talking about physics(yes her momentum counts, OK 1 point) as well as The friction (grip) between her hand an pole. Also biology (balance, reaction time) and chemistry (alcohol content if applicable). I am sure that I haven't thought of some stuff since I am writting fast, but please add. Anyways the point is, The reason that she fell is not properly represented here, and therefore the science in play is flawed. Good idea though, like the concept.

[CJ]

So is this what engineers argue about after work on Friday nights??? Impressive yet a bit confusing- what about her boobs????

[LowProductivity]

no, I think this is what engineers argue about during the day (in this case thursday) when they should be working. Anyway I agree with that last guy in that I'm not sure her rotating around the wall had anything to do with the fall. Looks to me like she just fell backwards off the step. Also she sucked at pole dancing anyway, so who cares?

[A girl]

You're mean. Don't you have any real science to make fun of?

[atouk]

When she leant to the right as she arched her back in a different direction, the arc of momentum of her implants reached critical velocity, thus causing a shift in the surrounding space/time continuum.

She didn't fall down, her mass jsut shifted in a direction equal to the change in localized gravity.

Next week: Alcohol use and it's effect on centrifugal momentum.

[neb]

if a drunk slut falls in the middle of the woods and theres no one around does she make a sound ? this website is lame!

[holly]

funny -- great feature!

[Phil Plait, aka The Bad Astronomer]

The center of rotation statement is in fact wrong. The center of rotation stays put, but as the mass of her arms comes in *closer* to the center of mass/rotation, the rotation rate increases.

[paul]

A few comments.

(a)
The center of rotation would change. Take a simple example: A ball tied to a rope spining around a post. The post is the center of rotation. Now introduce another post 9/10 of the distance from the original post to the ball. The ball will now spin around the new post, and have a new center of rotation. Similar thing happening here.

(b)
It is most likely the case that the girl falls due neither to her contact with the wall, nor her loosing her footing. The most likely explanation is that the girl falls due to her inability to grasp the pole firmly enough while executing an increased rotation rate. Her grasp is weaker than the centripetal force during her increased rotation rate.

There is actually evidence in the video for this conclusion as well:

(1) Her fall is a smooth motion, rather than horizontally jerky as would be required by hitting the wall, or vertically jerky as would be required by a miss step.

(2) Before contact with the wall, all of the tendons in her arm are tensed up indicating that there is a sudden, albeit too late, desire to grasp the pole more firmly.

[Timothy Logsdon]

I think the argument is valid, although I think some people may have misunderstood it. Just before coming in contact with the wall, her fulcrum is at her right hand. She started rotating around the pole and struck the wall with what appears to be her left hand and somewhere in the vicinity of her hips, which is probably under her center of mass. Since she obviously didn't have a very tight grip on the pole, it slipped from her hand, and she pivoted around the corner of the wall. Since her body was moving in a somewhat consistent angular velocity, when she struck the wall, her upper body had a higher moment of inertia than her legs, resulting in the net force that reduced the downward force her feet had on the floor and moved her center of gravity to a point that was not above her feet. The net result was that she rotated around the corner of the wall.
This was a fun distraction, but I need to get working on my vector mechanics homework. ;o)

[kev]

Ya ya her fulcrum changed and I'm sure using the formula 9.8 m/s to the 2nd power she hit the floor traveling no faster than 56 m/s. lol that shit was funny her drunk uncoordinated ass falling all over the place!

[Chris]

i think you guys are looking too far into this one.... here is the science, alcohol + drunk underage girl = drunken mishaps

[JIggleBilly]

Video has been removed due to copyright infringement. Awesome.

[CrackWilding]

Copyright infringement? Who are they kidding?