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A Physics Lesson For Pedestrians

Friends-Romans-Countrymen, Math and Science

This article was originally published by me in October 2011, but as I’ve been digging through old stuff looking for some gems from what I can salvage of the old site, this looked like it was worth bringing forward into 2014.

You can follow updates on the more hilarious/sad aspects of this topic at I don’t move out of the way for people walking with their head down.

Here’s a little lesson in physics. Bear with me, there is a point to this.

I am a large person. Blessed with some Nordic genes, I am 189 cm tall and tip the scale around 111 kg. I walk, due to long legs and general impatience, at about 6 km/h (1.7 m/s)over short distances… like coming out of the Subway with my lunch and heading back to work.

In motion, therefore, I have a kinetic energy of 0.5mv2, or 154 joules.

If you’re a more usual-sized person… say, an average woman (65 kg) walking down the street, at an average speed (4 km/h, 1.1 m/s) with your head phones on and head down so you can’t really see where you’re going, you have kinetic energy of about 40 joules.

So when you thud into me because you didn’t see me come around the corner because you weren’t looking where you were walking and couldn’t hear anything because you had headphones on, I feel an effect of slightly slowing my movement, while you experience what is roughly the equivalent of a light jog into a brick wall…

… and I don’t feel sorry for you.

Granted, the chauvinist in me feels a little twinge when a woman gets flattened in this way. It’s all I can do to resist bursting out laughing when some man, beetling along with his head down, gets flattened, however. Mostly, I just wish that people took more responsibility for watching where they’re going. I do my damndest not to run into people, but there’s only so much I can do when people are wandering around deaf and not looking where they are going.

In my whole life, I’ve only ever lost one encounter – I was walking with my head down and ran into someone substantially bigger than me. That was a lesson I never forgot. If you don’t want to land on your arse, I suggest you learn the same lesson: Pay attention to what’s around you.

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