Confusion on Newton's 3rd law!! According to the 3rd law, the equal and opposite forces are acting on two different bodies and therefore cannot cancel each other. They are mutual forces. Why then, so we say the force of gravity on say, a book on a table, and the normal force acting on the book by the table, is an example of the 3rd law? They are forces acting on one thing (the book) and are not triggered by each other. Also, hence they cancel each other out. So how is it an example of the third law?