Why should a tractor, driving a car in tow, not change its speed abruptly?

If the tractor brakes sharply, then the machine will crash into it, if, on the contrary, it accelerates sharply, then the cable connecting the machine and the tractor will burst. The reason for this is the phenomenon of inertia, that is, the body maintains speed in the absence of the action of extraneous forces (the body moves by inertia until the friction force of the wheels on the road in this case exceeds the inertial force) The same phenomenon is observed when the cyclist sharply brakes , after which it flies out through the steering wheel.