May 13 2007
Physics 101
The railroad bridge over Washington Street here in Ann Arbor is unusually low, so two or three times a year an inattentive truck driver receives a very sudden lesson in Newtonion physics.
The inattentive truck driver learns about two laws of physiscs. The first is the one which holds that two objects cannot occupy the same space and the same time. The second is the law of inertia, which is demonstrated by objects in the cargo area continuing their forward motion even though the truck has suddenly stopped, until their motion is arrested when they slam into the front wall of the cargo box. Thus does the bridge educate the inattentive truck driver.
Those of us who work near the bridge have learned to recognize the sound of the bridge giving a physics lesson. It is a metal-on-metal grinding, tearing, ripping sound, followed by an eerie silence while the inattentive truck driver contemplates Newton’s laws and his suddenly narrowed employment options.
It takes some work to extricate the truck. A large wrecker of the kind used to tow semis, is summoned. The air is let out of the stuck truck’s tires, and then the wrecker drags the truck from under the bridge. Sometimes it takes two wreckers.
Not a lot of work gets done while this happens.