The plane is vibrated at some specific frequency. The waves travel across the plane and at some places they add together and at other places they cancel out. Where they cancel out the salt stucks because there is no vibrations and at other places it just gets vibrated away.
It's Never too Late to Study:http://www.FreeScienceLectures.com
Notice: This video is copyright by its respectful owners.
The website address on the video does not mean anything.