On September 12, 1999, about 1915 Eastern Daylight Time, a Piper PA-22-108, N5125Z, was substantially damaged while landing at the Whitman Airport, Manassas, Virginia. The student pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the instructional flight conducted under 14 CFR Part91. The student pilot stated that he was conducting touch and go landings on Runway 4, a 2,450-foot long grass runway. After the fourth touch and go, the pilot returned to land on Runway 22. Realizing that he was too high on final approach, the pilot slipped the airplane to increase his decent. A recovery from the maneuver was not preformed, and the airplane touched down hard on the runway. The nose wheel then collapsed, nosing the airplane over inverted. The winds reported by a nearby airport, at 1855, were 150 degrees at 6 knots.