Level 14
The layout of this level might be a little misleading. The temptation is to try to bridge the gap for the ball to roll across, but there's no need. Stack two square blocks precariously to the left of the gap, and on the other side place the thin block vertically so that it falls onto the red button.
Alternative solution
Yashar Kamyar also sent in this better solution:
Christoph Kment gave us this ingenious two-step way of doing it. In the second step you pull out the thin piece:
