Why does the motor start to rotate in a different direction?

Question

Electronics

Welcome all! The question is probably in its own way stupid and a little off topic, but still.
A little background: I have a Chinese wind blower heater, well, I think everyone has seen such. If anything, under

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photo (I have the same appearance, only the "firm" is different). So, during operation, it rotates in one direction, then in the other. (roughly speaking, 180 degrees back and forth). Today there was a small technical breakdown, but I was interested in the principle of its rotation - how does it start to rotate in the other direction?
I dismantled it all, inside, to my surprise, there was nothing but a button and an engine. Now about the engine. As I understand it, this is a synchronous single-phase AC motor, with a permanent magnet as a rotor. (I hope I phrased it correctly). It spins slowly due to the block of gears (ala watch), it also has a winding and, in fact, the magnet itself. Nothing else. Powered directly from 220V.
So, if you clamp its rotor (in other words, the gear that sticks out of its body) with the same pliers, then within a couple of seconds it will change the direction of rotation.
Since I am not particularly strong in knowledge in this direction, the principle itself is not clear to me. I don’t even know what to google ... In general, the question is: why does it change direction?
Please, if possible, explain "on the fingers")
Thank you in advance.

Answer 1

I hope you are aware that 220v 50 Hz means that the voltage polarity changes 50 times per second.
It changes directions depending on at what point in time you turned it on and which half-cycle is positive or negative at the moment in the 220v network.