Newton's Third Law for Normal Force

Question

We're learning about normal forces and I came up with the following scenario. Its conclusion doesn't make sense, and I was wondering where I went wrong in my assumptions?

If you put a book on a table, the table exerts a normal force on the book, the book in turn exerts a normal force on the table (Newton's Third Law). If the normal force exerted on the table by the book were N_B, the weight of the table were W_T, and the weight of the book were W_B, would the force that the table exerted on the ground be N_B + W_T + W_B?

This really confused me because the force exerted on the ground by the table would increase by twice the weight of the book, which makes no sense.

Answer 1

If you draw a free body diagram for the book, the forces acting on the book are its weight (downward gravitational force) $W_B$ and the upward force exerted on the book by the table $N_B$. So the force balance on the book is $$W_B-N_B=0$$

If you draw a free body diagram for the table, the forces acting on the table are the downward force of the book $N_B$, the weight of the table (downward gravitational force) $W_T$, and the upward contact force of the ground $W_G$. So, the force balance on the table is $$N_B+W_T-W_G=0$$

When you do a force balance on a body, you include only the forces exerted on the body by other bodies, not the forces exerted by the body on other bodies. A free body diagram on a body helps you immeasurably in identifying the correct forces to include.

Answer 2

No, the force exerted downwards is just the weight of the table and book together. What you called N_B is W_B.