Which is an example of a movable impact surface?

A window sash is indeed an example of a movable impact surface because it is a part of the window that can be opened and closed. This movement creates a potential for impact during normal use, particularly in residential environments where children may be present. The ability of the sash to slide or swing can expose painted surfaces to wear and tear, leading to the potential release of lead dust if lead-based paints are present.

In contrast, a fixed window remains stationary and does not move, thus it cannot be classified as a movable impact surface. Similarly, an immovable wall does not allow for any movement, and a ceiling fixture is typically secured in place and does not involve direct impact potential in the same manner as a window sash. Therefore, the window sash is the most fitting example of a movable impact surface, as it encapsulates the characteristics needed for this classification.