How far the pendulum is in each direction, x being distance to center (what do you call place where a pendulum rests?), and y being height or something? That doesn’t make sense, cuz then y = 0 (I’m assuming if the height = 0, then the pendulum is at its “lowest point” in the center, ie aforementioned at rest place) at a bunch of x distances?

Unless they’re vectors?

Hmmm… if x is like, velocity going in the horizontal direction, and y is velocity going in the up and down direction… if x is 0 that means it has reached its highest “swing” point on either side and at that point the y will be the biggest it’ll get… and if y is 0 that means at that point it’s probably at the lowest and only going horizontally…

Time-derivative is velocity, right? So x dot is a shorthand for dx/dt, which is just velocity, and x double dot is d2x/dt2, which is just acceleration, then… never seen the dots before, so thank you =)

Also unfamiliar with calling velocity “time-derivative” but you call it that just because… that’s just what it is?

In physics is it useful to derive it by other things or something to find other stuff… I dunno… maybe some liquid is pouring into a container and it’s gaining mass over time or something, … I guess that would be a time-derivative too, though.