Pick the right statement about normal force: (section 5.7)
a. normal force is always perpendicular to the area of contact between an object and support
b. normal force is always antiparallel and equal in magnitude to force of gravity (weight).
c. normal force is always equal in magnitude to force of gravity (weight).
d. normal force is always antiparallel to force of gravity (weight), meanwhile its magnitude can be any.

A. Normal force is always perpendicular to the area of contact between an object and support.

Explanation:

Normal force is defined as the contact force. If there is no contact between the surfaces, they cannot applies a force which is normal on each other. For e.g, the surfaces of a cubical box and the cart cannot applies a force of normal on each other because of no contact.

If, when there is a contact between two surfaces they applies a normal force on each other, and this force is  perpendicular to the each other . This normal force is necessary to prevent object to penetrating into other.

an energy transformation flow diagram is shown

where is it ?

causes

fossil fuels burn

cities become more industrialized

human population grows worldwide