A group of physicists have discovered that they can make objects move against the direction of waves by using a tractor beam on water, which generates waves. This has important real-world applications, including confining oil spills. The physicists do not yet know mathematical theories explaining how it works. Dr. Horst Punzmann said " . . . anyone in the bathtub can reproduce it. We were very surprised no one had described it before." His group determined which frequency and size of waves in a wave tank could move a ping-pong ball where they wanted.
http://phys.org/news/2014-08-physicists-tractor.html
http://phys.org/news/2014-08-physicists-tractor.html