The armature of the motor is heavy so its inertia smooths the fluctuations in torque.
guru, are you saying the website isnt realistically correct?
The animation on the website is simplified to aid understanding.
The half-sine waveform of torque represents the INPUT to the rotor.
When the motor is unloaded, ie not driving an external mechanical load, all of the available torque will be used to accelerate the rotor, and the rotor will increase its angular velocity (spin faster) until the drag from windage and friction matches the torque and the rotational speed will stabilise.
When the motor is loaded, ie the rotor is driving some mechanism, the rotational speed drop and the available torque will be split between accelerating the rotor and accelerating the load.
When the system has stabilised, the torque available to drive the load will vary as the rotor turns, but will not fall to zero because in a practical motor the rotor has mass and that rotating mass will have inertia which will provide torque to the load during the time when there is no torque from the electrical system.
Note that this two pole motor has a BIG problem from a practical point of view, if it is stopped at the zero torque point in its rotation,
it can never start again without an external push.
This is why all practical motors have more than two poles.
Also note that the two pole motor will have very bad torsional vibration, not desirable if we want smooth running.
JimB