Magnets+

Imagine a board with magnets. Your goal is to put the blue-colored negatively-charged magnets into a certain position on the board, using only magnetic forces and gravity. This is both a puzzle and physics game, combining learning and fun with magnets. While designed primarily for children, you will find it fun as a grown-up.

The game has 20 difficulty levels. You start on level one, the simplest. As you earn more points, you move to next level, a bit more difficult than the previous. Each 12 points earned move you to the next level. 

This is mentioned in the game itself, but worth repeating: use settings screen to control game parameters (see also "Presets" button, which gives access to several preset parameters).

Also, a paid upgrade (within this game itself) gives you full control over gravity and magnet strength, otherwise fixed.