Final answer:
Diagonal lines are used to convey a definite forward or backward movement in visual art, representing motion and action dynamically. Artists use line quality to further depict movement, with contour lines enhancing the sense of motion in characters or objects.
Step-by-step explanation:
The type of lines that have a definite forward or backward movement are diagonal lines. These lines are perceived as the most active and tend to represent movement or motion, especially in visual arts. Unlike horizontal lines, which create a sense of calmness, or vertical lines, which convey stability, diagonal lines are dynamic and can depict objects in a state of action or forceful movement. This principle is used both in natural scenes, such as in the arrangement of tree branches, and in constructed environments like architecture. When an artist wants to portray motion, such as a character running, they may use a diagonal line to suggest that the character is leaning forward and about to burst into action.
In art, line quality also contributes to how movement is perceived. Geometric lines, like straight or zigzagged ones, can convey structured motion, while organic lines often imply a more fluid, natural movement. Hence, artists often use a combination of contour lines and diagonal lines to create a sense of motion and direction in their work. For example, motion lines in comic strips are often used to indicate the direction and speed of a character's movement.