Play Sliding ball gem puzzle (Inertia) online Works — plays right here, unlimited puzzles
Guide updated October 2026 · Runs via WebAssembly (native port)
Inertia is a sliding puzzle in which you move a small green ball around a grid of walls, gems, mines and stop squares. Once the ball moves it keeps going until something halts it, so you plan routes rather than steps. The goal is to collect every gem without touching a mine. The puzzle is ready below; use the numeric keypad or click in the direction you want to go.
Controls — what does what
| Action | Keyboard | Mouse / touch |
|---|---|---|
| Move in a straight line | Arrow keys or keypad 8, 2, 4, 6 | Click on the grid in that direction |
| Move diagonally | Keypad 7, 9, 1, 3 | Click on the grid in that direction |
| Follow the hint arrow (after Solve) | Space | - |
| Back up after hitting a mine | U or Ctrl+Z | Game menu, Undo |
| New puzzle | N | Game menu, New game |
FREE This is the complete game, free. Open source under the MIT licence: the complete puzzle, with a new grid every time.
Inertia is from Simon Tatham's Portable Puzzle Collection, © Simon Tatham and contributors, used under the MIT licence. Built from source by scripts/build-puzzles.mjs.
How to play
- The ball moves in any of eight directions, straight or diagonal.
- It keeps sliding until it hits a wall or lands on a stop square.
- Gems are picked up as the ball passes over them; they do not stop it.
- Moving diagonally, the ball slips through a gap between two diagonal walls without stopping.
- Touching a mine ends the game, even if the same move took the last gem.
Sizes and difficulty
The Type menu offers 10x8, 15x12 and 20x16 grids. There is no difficulty setting; larger grids have more gems to collect and longer routes to plan. Custom sets any width and height.
Solving tips
Find the stop squares first: they are the only places mid-board where the ball can rest, so a route is really a chain of stops. Gems lying along a wall are usually easy; the ones in open space need a stop or wall beyond them. If you hit a mine, Undo puts you back before the move, and the game keeps a count of your deaths. The Solve option shows a hint arrow for the next move rather than solving the whole board.
Where this puzzle comes from
Inertia is part of Simon Tatham's Portable Puzzle Collection, a set of about forty logic puzzles written by Simon Tatham and contributors and released under the MIT licence. Every grid is generated on the spot, so the supply never runs out, and for the grid-logic puzzles the generator makes sure each has exactly one solution, reachable by reasoning rather than guessing. The version here is the collection's own code compiled to WebAssembly; the Game menu can save a puzzle to a file and load it again, and the Type menu changes the size and difficulty.
Frequently asked questions
What happens if I hit a mine?
The ball is destroyed and the game ends, but you can choose Undo to go back to before that move. The game counts how many times you do this.
What does Solve do in Inertia?
It works out a route that collects all the remaining gems and shows an arrow on the ball for the next move. Pressing Space follows the arrow one move at a time.
Is Inertia free to play here?
Yes, with no limit on the number of puzzles. Inertia is open-source software under the MIT licence, and every grid is generated fresh when you press New game.
Does it work on a phone or tablet?
Yes. A tap works as a click and the puzzle resizes to fit the screen. Puzzles whose controls use the right mouse button are easier with a mouse.
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