A 1.75 kg book is sitting on a stationary table. What is the magnitude and direction of the force exerted on the book by the table?
The force exerted on the book by the table refers to the normal force `F_N` .
Note that a normal force is always perpendicular to the surface of contact. It is always directed upward, too.
Since the book is lying on a stationary table which means that the surface is horizontal and not moving up or down. So normal force `(F_N)` is equal to downward force which is the weight `(W)` of the book.
Moreover, since the book is at rest the forces acting on the book are `F_N` and `W` only.
Using Newton's Law,
`sum F = 0`
Since `F_N` is the upward force and `W` is the downard force, their signs differ.
`F_N - W=0`
Note that weight is the product of mass of an object and gravity. The value of gravity in earth is 9.8 m/s^2 .
`F_N = (1.75 kg)(9.8 m/s^2) = 17.15 N`
Hence, the force exerted on the book by the table is 17.15 N and is directed upward.