Simulating an object oscillating with SHM in GeoGebra is easy but simulating a pendulum is tricky. The problem is that a pendulum bob moves in a curved path. A maths teacher friend of mine once showed me his pendulum simulation, he had done it by making the angle vary sinusoidally, it looked OK but didn't really move like a pendulum. The pendulum actually ony moves sinusoidally if the swings are small, if we resolve the forces we find that the horizontal component of tension is proportional to the horizontal displacement. The horizontal component of these pendulums motion is sinusoidal, the curved motion is made by plotting the intersection between a vertical line and a circle. 9 pendulums in 3D took some time.

I always used to say pendula until I read that "The Oxford English Dictionary admits pendula as rare and archaic". The reason people often say pendula is because of some rule associated with Latin words. I've never studied latin so don't know why I adopted this rule, must have been my dads doing. Apparently pendulum isn't a Latin word so Latin rules don't apply. In any case, if that was a rule then the plum tree in my garden looks likely to produce a lot of pla this year