Random Floating Gravel

If I use a piston to push blocks of gravel of the edge of a cliff they randomly float and don't fall like usual.
To repeat do the following.
1.place several pieces of gravel in front of a piston
2.create a pulse system using redstone repeaters.similar to that shown in the video created by sethbling and grum.
3. power the piston using the previous pulse system.
4. watch as the gravel that has been pushed by the piston isn't affected by gravity