# Talk:Railroad

One of the questions is friction. Railroads can only travel up very low grades, and this should be even worse on Mars. As F=uN, u being a property of materials remains the same, but N is reduced by the lower gravity. N is a form, and F=ma. m in invariant, but a, the acceleration is proportional to gravity. So trains will have less roll resistance and can be larger, but will have trouble going up steep grades.

Air resistance is scarcely a factor, so the two main elements in a train movement will be roll resistance and acceleration up to moving speed. If regenerative braking can be used, then the main factor would be reduced to roll resistance, as stopping the train would return the energy that was used to accelerate it.