See the PBS SpaceTime explanation hyperlinked-to elsethread and then the Physics StackExchange one. Gravity "pulling on" rock and water differently is a misleading explanation, and really an attempt to tweak an explanation that is bad to start with.

Tidal forces are fictitious forces that are what orbital mechanics look like in the accelerated frame of reference of the thing doing the orbiting. They are not a uniform "pull" in a single direction. That will get you to the idealized Waterworld explanation of PBS SpaceTime. What will get you further is the realization that PBS SpaceTime is almost on-point with the "assume a perfectly spherical cow" joke, which is where the Physics StackExchange explanation comes in, with the reality that the water is moving around and over the rock and that it's a lot more complex.

Which then gets you to Tom Scott and part of Cornwall rising and falling twice per day. (-:

* https://youtube.com/watch?v=lCA0II1sVZA

Thankyou. I will read up on this!