Okay so I was confused by this too. I think it is especially especially deceiving because it specified that the ball only moved in one axis of motion, but it's

Okay so I was confused by this too. I think it is especially especially deceiving because it specified that the ball only moved in one axis of motion, but it's actually two (falling, and then rolling over). I also tend to get very frustrated with articles when they do a terrible job of explaining things, because it can feel like an impassable wall for the reader, where they just stop and don't continue. But in this case, they made up for their (really really) terrible wording with a (really really) clear image describing exactly what they meant. It did take like a minute of staring at the image to figure out what they meant, but sorry, this is a blog post about math, that's what it's going to take regardless. It's unfortunate that they couldn't communicate their thoughts more, but it's kinda brutal to just stop reading because of one sentence, when they put all this effort into making a diagram to explain that one sentence