Final answer:
The plumb line should fall equidistant between the knees when standing, and deviations may indicate alignment issues. Variations in posture can affect alignment, and the concept of a line of feet refers to the stance affecting the plumb line's position.
Step-by-step explanation:
When examining the relationship of the knees to a plumb line, a plumb line is expected to fall equidistant between the knees when a person is in an anatomically correct standing position. Common faults in this alignment can be observed when the plumb line does not fall centrally, indicating potential postural or musculoskeletal issues.
Variations in a person's stance, such as sitting or kneeling, can also affect how the plumb line relates to the knees. For instance, a photographer may brace an arm and elbow on their knee to keep the camera steady, shifting the plumb line's position. Additionally, when referencing a line of one foot or more, we are discussing the line created by the feet and the effect of standing on one or multiple feet and their spacing on the alignment of the plumb line.
Measuring the angle between a line and a plane, like the plumb line and the hypothetical plane between the knees, is a technique often used in biomechanics and kinesiology to assess body alignment and posture.