Saturday, June 29, 2013

Citi Bike is failing at physics

It seems that New York City needs to take some remedial STEM – the promotional materials for NYC BikeShare have an elementary physics mistake.

Their marketing materials state:
[the bike] has a low center of gravity for a more stable ride.
It turns out that a moving bicycle, is actually less stable when the center of gravity is low. Much like a balancing a pencil (low CG) is harder than balancing a broomstick (high CG). This phenomenon is explained well in this article about robot bicycles.
I emailed citi bike to complain and they responded with this:
I'm fairly certain that the engineers involved in constructing these bikes have looked at the pros and cons of both high and low centers of gravity, and found this to be the best option for the widest range of people.
I cannot argue with this. I've ridden these things in Boston and in Washington DC and they are indeed very stable; nicely done engineers! The stability has absolutely nothing to do with a "low center of gravity." In fact the stability to ride might actually be due to a high center of gravity for bike+person compared to more aggressive bike frames.
The next thing citibike said was:
Besides, almost anything with a lower center of gravity is going to be more stable based on simple physical laws.
Correct and irreverent again. Objects siting motionless on the ground will be more stable with a low center of gravity. But bikes mid "ride" are more like an inverted pendulum than a stable object. Here are some suggestions for a new description.

I wouldn't normally be so fast to recommend remedial classes ... but just last march NYC made a subway poster which mathematically embarrassing at best. Also, several years ago Eli previously discussed the state of science education in NYC which left much to be desired.

I'll end this post with a snobby message from Boston: get it together New York!

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