* Normal Force: The component of the reaction force that is perpendicular to the surface is called the normal force. It is the force that prevents an object from falling through the surface.

* Friction: The component of the reaction force that is parallel to the surface is called friction. It opposes the motion or tendency of motion of the object along the surface.

Examples where the reaction force is not perpendicular:

* Object on an inclined plane: When an object rests on an inclined plane, the reaction force has both a normal component and a frictional component. The normal force is perpendicular to the surface, but the frictional force is parallel.

* Object pushed against a wall: If you push an object against a wall, the reaction force from the wall will be perpendicular to the wall only if you push directly into it. If you push at an angle, the reaction force will have a component perpendicular to the wall and a component parallel to the wall.

* Sliding friction: The force of friction acts parallel to the surface and opposes the motion of an object sliding across the surface.

Conclusion:

The reaction force on a surface can have components both perpendicular and parallel to the surface. The perpendicular component is the normal force, and the parallel component is friction. The relative magnitudes of these components depend on the specific situation and the forces involved.