Algodoo

when you dowloaded the scene you see there is a 6.0kg steel ball and a wooden panel.
It looks very normal but when you play it,the ball appears to goes up slowly.
How did it worked?(use this to make your kids or friends amazed or upload a youtube video so i can see how do they react)
PS:
to someone who knows, PM me so no one can know how it worked.

good luck