The ball should have "Dynamic" physics. That's so it can bounce against the wall elements, which are "Static" elements. (The walls shouldn't move.)
http://brm.io/matter-js/docs/classes/Body.html - If access to Matter.js was unrestricted, it's simply just a use of the Matter.Body.setAngularVelocity(body, velocity) API.
No changes of the current version of the book are planned. Adding video makes the project massive, so that's why it's a new project. So far, people unanimously want video...
So I figure I'd create new examples and then just do a video for each section, explaining what that section is about. I'm realizing that people don't like to read. Although, trying to learn from a video can also be annoying. So the idea is that both options are available. A video could very likely be a read-through of the section.
I haven't started that though. It's a huge project and I don't know what's up with Hype 4, so I'm working on a Hype scripting project right now.