# The Physics Behind “Unstoppable”

Can they stop the train loaded with hazardous chemicals before this “missile the size of the Chrysler Building” hits a populated area and “vaporizes everything in front of it?” That’s the big question that drives along the plot of the new Denzel Washington thriller, Unstoppable. If you don’t believe me, just watch the trailer above. Now we get all academic on you and ask: Is that train really as powerful as a skyscraper-sized missile? And then we turn to Emory physics professor Sidney Perkowitz for the answer:

Perkowitz is a good person to size things up. He’s not just any physics professor. This physics prof wrote the book Hollywood Science: Movies, Science and the End of the World and he sits on the advisory board of the Science and Entertainment Exchange, a National Academy of Sciences program that tries to bring more scientific accuracy to mass market entertainment. Thanks Stephen for the good tip here …

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• DefaultProphet says:

I thought the danger in the movie was the cargo, toxic materials.

• Tanner says:

So… something about 1 million pounds didn’t sound right to me. I did some investigating. Here’s what I found:

“The heaviest train was a BHP Iron Ore train weighing 79,577 tons. The 10
locmotives and 540 ore cars ran from Newman to Port Hedland, Western
Australia, a distance of 253.9 miles, on May 28, 1996.

Do a little rough math and this comes out to 160 million pounds. Then being that I’m an engineer and somehow find stuff like this fun I looked up the energy in TNT (4.184 MegaJoules per kg) and using his numbers determined that the velocity he used was less than 10 mph (4.29 meters/second). He even says himself how important the velocity is because that term is ‘squared’. I make no claim of being smarter than this physics professor but I decided to re-run the numbers…

Using 160 million pounds and 60 mph gives an energy just shy of 7 tons of TNT!

Granted it’s in a different form… a train crash’s energy would be released comparably much more slowly that TNT will ignite… but still! Sorta cool! :)

• Redlami says:

What about the highly combustible cargo and the diesel fuel on board? I would think that the explosive release of all that potential energy should enter into the picture as well.

• Dan Colman says:

Yes, it does seem that he left the chemicals “out of the equation” – pun somewhat intended. That could change things, couldn’t it?

Dan

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