There are many sources of vibration capable of producing motion sufficient to be perceptible by the occupants of a modern building. Transportation-related sources such as trains, subways, buses and trucks are common external sources of irritation. Often, internal activities such as aerobic exercises, use of indoor tracks or corporate weight rooms can introduce vibration into one part of a building, which is felt elsewhere, producing bewildering periodic problems. Problems also arise from vibration introduced by rotating mechanical equipment in basements or mechanical penthouses. These dynamic situations are difficult to predict with static design methods.