Basically every vehicle has it but in trains/trams is it particularly strong (probably because they have so much mass).
In: Physics
Yes , it is called inertia. According to newton’s law of motion, a body will continue to have its momentum (m*v) unless it is applied a force to change this. In terms of trains, trams the braking applies the force and thus the train stops but you who was moving along with the train did not have any force acted on you, due to which you feel the bump until friction, or some other force helps you stop. This lag in coming to zero speed is the bump you face
What you are feeling is “jerk” or the change in acceleration. It’s the same sensation when someone suddenly slams on the throttle or brake.
This occurs when a vehicle comes to a stop because brakes only help decelerate when the vehicle is moving. When the vehicle comes to a complete stop, the acceleration goes from {some big negative number} to zero almost “instantaneously” (over a small time); imagine the time it takes for the vehicle to go from 0.1kph and to 0kph.
Jerk = change in acceleration / time.
= {some big number} / {small time}.
= {some bigger number}
This jolt can be explained by a property known as jerk. Just like acceleration is how fast you are changing speed, jerk is how fast your acceleration is changing.
When a vehicle is slowing, it is typically done at a constant rate of acceleration, for the comfort of the passengers. However, when the speed reaches zero there is a sudden change in acceleration from the rate you were decelerating at to an acceleration of zero (You do not start moving backwards, which would happen if you maintained constant acceleration). It is this jerk that you are feeling.
Brakes use friction to stop a vehicle. The tiny jerk you feel at the end of a stop are the brakes locking up. Although engineers design brakes using materials that have a relatively low static friction relative to sliding friction, static friction will always be higher that sliding friction, so at some point while slowing, they will “grab” and the vehicle will stop more suddenly. That sudden stop is almost imperceptible because you were already moving very slowly by the time it occurs, but it does occur.
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