Book Cart opens in the Lab: change the number of books, the bindings, gravity, wind and more, and watch the live physics. When you want a challenge, press 🎮 Play the game. The books start hanging from the cart; swing them up and keep them balanced above the cart, or, for a harder goal, stand every book straight. The first levels are gentle, with a wider balance band, a shorter hold and a helping hand you can turn off. Pick any level, and slow motion or real time, in the menu (☰). Phone or mouse: press on the scene and slide left or right; the cart follows your finger. Keyboard: hold ← → (or A, D) to slide the cart, P pauses, R starts again, O turns the autopilot on or off, I shows the physics. The physics behind it →