UP News
 
   
   
   
   
Editor-in-Chief:
James Stankowicz
Assistant Editor:
Steven Hochman
Layout Director:
George CB Ling
Online Editor:
Steven Hochman
Staff Writers:
Victor Albert
Brady Nash
Eric Swanson
Faculty Advisor:
Dr. Amlan Biswas

 
   
Physics of Breakdancing
by Harold Rodriguez

Note: This article is continued from the previous issue.



With legs apart, he will then push as hard as he can against the ground with his right hand. This will provide lift equal to, but hopefully much more than: mg minus the upward force provided by his back-swinging left leg. With this left hand, he adds a bit of extra lift, but more importantly, extra rotational inertia by pushing off at an angle. The breaker attempts to increase his rotational inertia by spreading his legs out as far as possible, as they naturally circulate around. If we let d be the distance between the breaker’s legs while they are most apart, the breaker’s rotational inertia will be given by, roughly: Ibreaker = (3/10 m(d/2)2) (assuming the breaker is a perfect cone, which most are).

If performed with great timing, the breaker will “pop” into the air. See [Figure 2].



Here, the breaker has nothing but the force of gravity acting, and thus cannot change his angular momentum. But just like a falling cat, there must be some way to turn over, despite having constant angular momentum. The trick lies in changing your rotational inertia (by changing the orientation of your limbs, etc.). Since angular momentum is constant, angular velocity must change correspondingly (since L = const = I ù); thus, retracting limbs can allow the breaker to turn-over to an agreeable angle. In the best situation, however, the performer will have provided so much initial lift that he may “reach” across and land on his other hand. See [Figure 3].



The breaker can only get to this stage if he recalls: “things that spin quickly and have large rotational inertia are hard to stop”. The rotational inertia of his (presumably heavy and long) rising leg causes a net force upwards, while the other provides a horizontal twist. Let’s assume the breaker remembered and got to this stage successfully; informally: hand = on floor. If one were David Griffiths, one would formally overanalyze this. Perhaps: if the integral over a closed Gaussian surface bounded by the skin of the breaker equals the enclosed quantity of the blood of the breaker:



the breaker has performed the move correctly (or at least hasn’t bled all over the place). Lastly, from here, the breaker must use the rotational inertia of his legs to propel himself into a position similar to that of [Figure 1], and then repeat the process ad pwndium.