Question

Where normal reaction is not perpendicular to surface?

Answer 1

The normal force is always perpendicular to the surface with which a body is in contact. For a body on a sloping surface (say a ramp) the normal force acting on that body is still perpendicular to the slope.

Answer 2

This is the contact, and it can, in principle, point in any direction into the other surface. The component that is parallel to the surface is called “the friction force”, and the component that is perpendicular is called “the normal force”. Thus, the normal force is always perpendicular to the surface by definition.