Friday, 1 February 2013

Why is the bridge black?

Lethbridge's High Level Bridge after snow, January 2013, photo by Belinda Crowson

Last week, on a break between classes, I had the Ipad with me in the Galt Viewing Gallery and was able to snap this photograph through the window. I often talk about this scene but don't usually have a photograph to highlight the answer.

Why is the High Level Bridge black? This is a question I pose virtually every week (and often several times a week) to the 1000+ grade 3 students who come every year for our Building Bridges school program. 

I have heard some incredible whoppers over the years for why the bridge is black. It looks better that way. You can tell from the old photographs that they only had black and white paint. It was a coal mining town and they knew it was going to get dirty anyways so they painted it black so the dirt wouldn't show. Black paint was cheapest.

Black gets hot and melts snow. I took this photograph just after the snow quit falling (before it quit falling you couldn't see the bridge from the Viewing Gallery to my consternation as I tried to get a class to imagine the bridge that was out there). The coulees are covered with snow. Yet there's no snow on the bridge. The black paint melts the snow and with all of the angles of the bridge, the snow slides off. It's a way to use science to remove the weight of the snow from the bridge.

If you'd like another stumper, how many triangles are in the bridge? I don't honestly know the answer to this one but I always tease the grade 3 classes that if they are ever really bad their teacher can make them come back and count the number of triangles. Honestly I hope that never happens because I would have to then also count them to see whether or not they were right. Or make up the answer. Hmmm?   

Construction of the High Level Bridge Galt Archives 19738126000

Construction of the High Level Bridge Galt Archives 19760234021

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