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Partially engineering, partially physics.
When a train accelerates, such as an MTM-MTM electric train (four motor carriages, two trailer carriages) where does the backwards force go? Is it mostly distributed by compressing the rails behind the train laterally, thereby using the weight of the rails as resistance, or mostly through the sleepers underneath the train, thereby using the ground as resistance?
The sleepers and spikes are a system to bind the rails to the ground and spread the loads from the rails over a large contact surface. The forces from the wheels on the tracks are transferred from the rails to the sleepers to the ground. Momentum is conserved when the train changes velocity, but the mass of the Earth is so large compared to the mass of the train that the changes in the Earth's movement are too small to detect.
