The normal force on the crate points upward, perpendicular to the floor. It is called the normal force because normal and perpendicular mean the same thing. The normal force is always perpendicular to the surface with which a body is in constact. In the case of our problem, the ship, we will pretend the ship is being pulled on a floor. Figure 4 Ship, with gravitational and normal forces.
Friction Related to the normal force is the frictional force .
The two are related because they are both due to the surface in contact with the body. Whereas the normal force was perpendicular to the surface, the frictional force is parallel. Furthermore, friction opposes motion, and so its vector always points away from the direction of movement. Friction is divided into two categories, static and kinetic. It is the force which makes it difficult to start something moving.