Final answer:
Not all contact forces are normal forces. Friction, also a contact force, is proportional to the normal force but not the same. Normal force is specifically the support force exerted by a surface perpendicular to the contact area.
Step-by-step explanation:
Not all contact forces are considered normal forces. While normal forces are indeed a type of contact force that acts perpendicular (or normal) to the surface of contact, there are other contact forces as well.
For instance, friction is also a contact force, which opposes the motion or attempted motion between two objects that are in contact, and is proportional to the normal force but acts in a tangential direction relative to the object's movement.
Additionally, when you push on a wall or a bat hits a ball, these involve contact forces, but not all of them are normal to the surface.
According to Newton's Laws of Motion, the normal force, denoted as N (not to be confused with the Newton unit for force), is the supporting force exerted by a surface when an object rests upon it, equal in magnitude and opposite in direction to the gravitational force (or weight) if an object is not accelerating vertically.
If you are standing on a scale in an elevator, the normal force will vary depending on the elevator's acceleration. For example, it will exceed your weight when the elevator starts ascending, and it will be less than your weight during a descent.
In the case of objects on an incline, the normal force is less than the object's weight since it acts perpendicular to the inclined surface, not directly opposing the gravitational force.
Newton's third law dictates that forces always come in action-reaction pairs, meaning that whenever you exert a force on a surface, the surface exerts an equal but opposite force upon you.