If Isaac understood, why don’t we?

If a body,  or indeed a railway train is travelling at speed, there are only two forces acting upon it; the engine’s torque, diverted through gears to the driving wheels providing the forwards motion, and inertia, which is the force attempting to keep that same railcar stationary. If a third force is then introduced, attempting to turn the railcars’ forward motion to one side, there is a set set of mathematical calculations which determines how much the railcar can turn without being overtaken by the first force, which is the momentum provided by the engine. If the momentum exceeds the mathematical certainty of the turning, or centripetal force, the rail car will come off the rails, and crash, owing to the force acting upon the railcar.


See the Wimbledon crash, where the driver fell asleep at the controls, and the speed of the railcar or tram was too great to let the railcar take the bend safely; or one of many possibilities why the Amtrak train failed, which is where the railcars’ speed was said to be possibly at least twice the set speed for the rails curving into the bend at that point.