Maybe this is just a guy thing but… In the city I live in we have a train that passes through town several times a day, usually stopping me going somewhere important! As I watch these, sometimes long, trains with multiple engines facing both forward and backwards… Made me wonder?
How does a locomotive ever get moving without its steel wheels just spinning out? How does it ever get any traction? And what’s up with the locomotives facing forward and backwards? We’ll it was time for me to solve this childhood mystery as part of my 100 Question Challenge.
The answer was a lot simpler than I had ever imagined… It all had to do with the difference between kinetic and static friction. Static friction has everything to do with the friction created between the wheels and track. While Kinetic friction has everything to do with the motion of two surfaces working together. In the case of a train this would be couplings between the locomotive and each car.
In an easier explanation… All the locomotive needs to do is to get the first car started. Then the power of the locomotive and the first car creates the energy to get the third car moving. So, at that point you have a powerful locomotive, plus another fully loaded car creating momentum to just pull one car. So that domino effect just continues. So, by the time the last car starts rolling it has the power of an entire train needing to get just get one car started… That’s why there is space in between the couplings. This allows each car to get a little momentum to help pull the next car. Theoretically, if all the cars were tightly connected the locomotive alone couldn’t generate enough momentum to pull a long train. In that case the wheels might just spin out if it could get them turning to begin with.
Now for the locomotives going both forward and backwards. As it turns out, the way the locomotives are designed it doesn’t care which way it’s facing. It seems to have the same amount of power regardless.
Due to the physics involved, it’s harder for a locomotive to get 5 cars moving than an entire train.
As an added bonus, how do they stop? Easy, each car has brakes. But even with brakes, it takes a long time and distance to stop all that momentum.