April 16, 2012

Physicist did NOT write mathematical study to get out of traffic ticket

Sometimes, I get obsessed by the silliest little details. For some unknown reason today, the story about the Physicist Using Math to Get Out of Traffic Ticket story was making the rounds on blogs and twitter again. Again? Yes, it first came around a little over two weeks ago: on April 1st. (There's your clue that it is a hoax.)

In the Physics Central write up of the "study" the author is quoted to challenge readers to find the flaws in his argument. I don't want to get into the math right now, since I don't really have the time. But, let's look at whether anything in the paper passes the back-of-the-envelope sanity tests.

1.) His acceleration/deceleration calculations are for constant acceleration of 10 m/s2 (first negative, then positive) over a time range from 10 seconds before approaching the stopsign and 10 seconds after.  So, ten seconds before getting to the stop sign he was going 100 m/s?  That's 223 miles per hour.  Kinda speedy for a Yaris, if you ask me.

2.) His negative acceleration of 10 m/s2 is about the same as the gravitational field constant. If we buy his argument in his paper of his speed being around 18 mph (8 m/s) when suddenly applying the brakes, then his stopping distance would have been 3.2 m, which is about 10 feet. That is right at the line of what we'd expect for a coefficient of friction between the road and tire of 1, which is awfully high, but not completely impossible.  It smells funny, but it doesn't fail the sanity check.  Although, I'm not sure I'd want to be in the car when braking that quickly.

3.) The positive acceleration matching the negative acceleration in magnitude, though?  Completely crazy talk.  The best acceleration of a Yaris has a 0-60 mph time of about 9 seconds, which is an acceleration of around 3 m/s2, and well under his estimated acceleration.

So, well played prank, Mr. Krioukov.  You've made crazy drivers everywhere think a little bit more about physics, even if you led them a bit astray along the way.

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