Normal Force

From Newton's Second Law,

the net force on an object that remains at rest is zero.

There must be another force on the object to balance the gravitational force.

For an object is resting on a table,

the table exerts this upward force.

The table is compressed slightly beneath the object, and due to its elasticity, it pushes up on the object .

The force exerted by the table is often called a contact force, since it occurs when two objects are in contact.

When a contact force acts perpendicular to the common surface of contact, it is referred to as the normal force .

A book is at rest on a table top.

F (G) and F( N) must be equal magnitude and in opposite directions.