In a little park at the entrance to the Williamsburg Bridge in Brooklyn, New York, there are often kids rolling around on skateboards, bikes and scooters. Looming overhead is an equestrian statue of George Washington at Valley Forge, swathed in blankets and sitting proudly on a horse with bowed head. One summer afternoon I set my camera on a tripod near the monument. I sat for hours collecting sequential still photographs of teenagers on skateboards, skating the length of the monument and attempting to land tricks off the end of the granite steps. The idea was to capture movement in …