GrrlScientistScience This article is more than 12 years oldBridge thermometer
This article is more than 12 years oldDid you know you can use a steel suspension bridge as a thermometer?San Francisco's Golden Gate Bridge is made of steel, so one would assume that it expands and contracts during the day as the ambient temperature changes, just like other metal objects. Because the bridge is very large, this daily expansion and contraction is probably easily visible, but how much movement is there?
The curators at the Outdoor Exploratorium wanted to measure the change in the bridge over time and as the temperature changes, so they set up a spotting 'scope near their facility, which is two miles away, and focused it on the bridge. This 'scope has a reticle that allows the observer to measure the bridge's movements caused by the temperatures that the bridge experiences. By observing the bridge on the hottest and coldest of days through this device, the curators found that the bridge deck rises and falls by as much as 4.9 metres (16 feet)! They also found that the thermal mass of the bridge – the time it takes the bridge's temperature to equalise with ambient temperature – lags ambient air temperatures by approximately two hours.
San Francisco's public TV station, KQED, produced a short video explaining this phenomenon:
The Outdoor Exploratorium is on Facebook and can also be found on Twitter @Exploratorium
KQED is on Facebook and they too can be found on twitter @KQED
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