Build a magnetic accelerator!
How to use?
Place two balls directly in front of the magnets, and roll another ball to them from the other side.
As the ball approaches the magnet, the magnet will attract it increasingly speeding it up. When the balls are colliding, the fast ball transfers its energy to the magnet, and the magnet transfers it to the balls on the other side pushing off the first one as a billiard ball. This ball is speeded up by the next magnet, so the transferred energy increases.