Golden Gate bridge as thermometer

June 18, 2010

The curators over at the Exploratorium in San Francisco had an interesting question regarding the Golden Gate Bridge:  It’s large, and made of metal, and so must expand and contract as it heats up during the day and cools off at night.  But in what way, and by how much?

It turns out that as the sun heats the cables that suspend the roadway they expand and the deck lowers.  As the sun sets and the bridge cools off, the deck rises back up.  At the outdoor exploratorium, two miles away from the bridge, they installed a spotting scope trained on the bridge.  The scope has a reticle that allows them to measure how much the bridge moves.  The answer? The total excursion of the bridge deck, from hottest to coldest, is about 16 feet! The thermal mass of the bridge means that the position of the deck lags the change in temperature by about two hours.

Public TV station KQED produced a short video explaining the phenomenon . If you live in the Bay Area, or plan to visit, be sure to spend some time at the Exploratorium and visit their temperature-measuring spotting scope.

Steve Ravet

DN Gadgeteer

ps:  Don’t miss entering your electronic gadget in the Gadget Freak/Make design contest .

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