An important characteristic of line is direction. Different line directions imply different moods, or feelings.
Horizontal- quiet or sleepy.
Vertical- potential of activity.
Diagonal- strongly suggests motion.
This (picture above) is diagonal line. The shape of the horse is in a diagonal position (rearing). This is a good example because this horse is obviously moving. (remember diagonal line strongly suggests motion.)
This is vertical line. The cat is sitting in a vertical position, which gives it the feeling that there can be potential movement. However, since the cat is currently just sitting there, its up to you to imagine what he does next.
This picture represents horizontal line, which represents quiet and repose. This is a good example because the shape of the womans body is in a laying position (horizontal) and you can tell she is quite content, peaceful even.