metric tons or close to a quarter million pounds and as this goes around the corner there's a lot of force trying to make it lean out from the tracks the faster it goes the more that force is pushing to the side. if the gravity is enough then it stays put, but what about the cars in the back there was a difference to passengers who said they felt like they were flying off the tracks. and a train in the spanish plane crash. all of that is why investigators from the very beginning are looking at excessive speed. >> tom foreman, thank you very much. let's talk about this now. george bible the author of train wrecks an engineering