BB Roll

BB Roll is the dexterity puzzle from the back of a drawer, rebuilt as physics. A dial, a few ball bearings, and the tilt of your phone.

ROLLED, NOT ANIMATED

A ball on a slope accelerates at five sevenths of gravity, because a rolling sphere carries some of the push in its own spin. It loses speed to friction and to the air, it climbs the lip of a groove only if it is moving fast enough, and it knocks its neighbours aside with the bounce its material would really have. Steel on plastic skitters. Nylon on wood crawls. Wood on wood barely wants to move at all.

FOUR LEVELS

Easy, medium, hard and impossible: two balls and one ring to three rings and five. Work every ball into the middle circle and keep it there for a second. The rings have gaps in them, and those are the way in.

PRACTICE DECIDES NOTHING FOR YOU

No objective, no preset. Choose the balls and the board, the friction, the sensitivity, how many balls and how far apart the grooves sit, and just roll.

A NEW MAZE EVERY TIME

The gaps are somewhere different on every board. One worth keeping can be saved by name and loaded again whenever you want it.

LEVEL IT WHEN YOU LIKE

Reset takes however you are holding the phone right now to be flat, so the dial never fights the way you sit. A calibration screen will time a roll and check it against the tilt if you want to see the working.

MORE

• Optional gyroscope, for a dial that a knock on the table cannot jolt

• No account, no sign-in, nothing to connect to

• Plays offline

• 25 languages

Free, with ads.