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Re: [Phys-l] Kinetic vs static friction



The newspapers recently featured the man who was the real-life hero of the incident, which happened in the 1990's. The real runaway train with 45 cars and the engine began at a yard in central Ohio when the engineer, as he was getting off for a break, hit the throttle instead of the brake. He hopped off and the engine started going, leading 45 cars on a chase down the stretch of track for over 40 miles. The engineer saw what was happening and tried to get onboard but slipped and fell off. The hero of the story happened to be at that yard bringing some kids for a tour. He was yardmaster at another rail yard and just, by fortune, happened to be there when the train started off without the engineer. He was getting a coffee when he and another man saw the runaway. They hopped into his car and raced off after the train following it for miles, watching it speed through intersections and helping divert traffic so the train could go by without hitting anything. Finally someone commandeered another engine, caught up with the runaway, and got the second engine attached to the end of the runaway. They reversed the second engine and applied the brakes getting the first train down to eleven mph. Our yardmaster/hero caught up to the train in his car, hopped onto the moving engine at eleven mph, and made it safely to the cabin where he was able to apply the brakes, stopping the train many miles from the starting point.
The yardmaster recounted the story to the papers: the incident was the basis for the movie. The producers of the film hired him as a consultant, but didn't invite him to the opening in Hollywood. However, a theater owner, knowing what he had done, invited him and his entire family and his friends to the opening of the movie.

Marty


On Nov 14, 2010, at 12:21 AM, LaMontagne, Bob wrote:

My wife and I saw a movie called "Unstoppable" this evening. The premise is how a run away train is stopped. It is based on a real event.

Modern locomotives have what appear to be a set of wings on the rear of the lococomotive with a large grille on top of the wings. These are used for "dynamic" braking. Basically the electric drive motors are run backwards as generators/brakes sending current to a huge array of resistors under the grille. This dissipates the energy as heat.

A key point in the movie is when a person suggests using this as the primary means of braking when a spare locomotive is attached to the end of the train to slow it down. He points out that the static friction of the rolling wheels is preferable to ordinary mechanical braking that would slide the wheels along the track when the wheels stopped turning. It was nice to see a movie get it right.

Bob at PC
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