Wednesday, 4 November 2015

This Post Is Not About Books

Promotional image featuring Wile E. Coyote
(Photo credit: Wikipedia)
The relief out there must be palpable.

Driving along the other day in Sharjah, doing bang on 99kph in an 80kph area. The guy in front of me's doing the same. We come up to a forward-facing radar (ie: it's facing away from us as we approach it.). These are a good thing, sportsmanlike and all that. You can see 'em, the game's fair, like. Not quite as sportsmanlike as the UK's stripy 'I'M A RADAR' decoration, but one takes what one can get.

Digression. What's not sportsmanlike is the Wile E. Coyote type who's taken to infesting the 'Middle Road' outside the new Islamic institutions that have been built on the brown field land that was Formerly The Sharjah Landfill. He's got a wee super-slim portable radar and he likes to slide it in behind sprinklers, discarded plastic barriers or road signs, then sit in his plain 4WD on the slip road and cackle insanely to himself as he waits to trap unwary motorists like a particularly obnoxious spider. Bad form, that man.

Anyway back to our 99kph drive. Guy in front comes abreast of radar and moves across into the slow lane and BLAM he's flashed. I drive past the radar at the same speed, and I'm good. I got to thinking about that as I've been flashed before doing under the limit but changing lanes. And I think I might be on to a bit of relativity in action here.

If you move away from the radar by changing lanes, you're compounding your speed relative to the radar by the speed of your lateral movement. That plus the speed of your forward movement means that although you are moving forwards at under the speed limit, you are moving away from the radar at beyond the speed limit. You'd have to be relatively unlucky, because the beam is reasonably tight for a radar working in what they call 'across the road' configuration. But travelling along that beam as well as across it means that, for the 0.2 seconds or so that the radar is sampling your speed, you're adding a couple of metres of travel at least. Even a metre of travel is equivalent to five metres per second, or 300 metres per minute. Or 18,000 metres per hour - 18 kph.

So by changing lanes in front of that radar, it's likely my buddy was actually doing something like 110 kph relative to the radar.

Einstein would have been proud of me, I'm sure...

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