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*