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As usual, I found myself watching quite a bit of YouTube over break, especially different BMX videos. While I could only dream of pulling off the tricks the professionals do, watching it makes me feel nervous as I realize the potential consequences of a nasty fall. I have kind of a lot of blogs on landings/falling, so I figure I will use this blog to tackle one of the most crazy things a bmx rider will do: grind a downward sloping railing on one peg. For those not extremely comfortable with BMX biking, pegs are a small metal attachment that can go on either side of the front and back wheels. BMX riders actually jump onto a railing, balance on one peg for a short amount of time before landing comfortably. They make it look easy, but there are numerous factors at play. First of all, the rider must have a clean takeoff in order to hit the railing in the desired location. Secondly, the rider must withstand the impact of one peg landing on the railing without causing the bike to rotate. Since a single peg is on a single side of the bike, landing on one peg creates a torque as one corner of the bike is on a stable surface while the other side is still in downward motion. It is up to the rider to shift their weight at the point of impact in order to offset this torque and remain balanced. Another component of the maneuver is to remain balanced on the rail throughout the entirety of the trick (even though they are not on the rail for long). You will see that riders will turn about 15 degrees from their impact time on the rail to the landing as the horizontal momentum of the back of the bike keeps going, since it does not have something to stop it like the front of the bike has the peg on the railing to stop the motion in that direction. Finally, the landing requires the rider to have a little "give" in his arms and knees, so the impact is not as strong as a force as it could be. Locking the arms or wrists often results in a broken wrist as the human body is not built to withstand large forces in recreational sports.

Here's a little video of some cool tricks that I couldn't even start to describe the physics of... 



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