AZING! How does the 3rd law explain the forces acting on a book on a table?

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Newton's 3rd law states that for every action, there is an equal and opposite reaction, which applies to forces acting on different bodies. The confusion arises when discussing the forces on a book resting on a table, where the weight of the book and the normal force from the table seem to cancel each other out. However, these forces are not examples of the 3rd law because they act on the same object, the book. The true pairs of forces are the book's weight acting downward towards the Earth and the Earth's weight acting upward towards the book, along with the contact forces between the book and the table. The equilibrium achieved is due to the table's elasticity, which creates a restoring force that balances the weight of the book, rather than being a direct application of the 3rd law.
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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?
 
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That is not an example of the 3rd law. The force pairs are:

1. weight of book towards Earth, and weight of Earth towards book
2. contact force on book from table, and contact force on table from book

The weight and contact forces of the book cancel for another reason: the elasticity of the table means that, as it is slightly deformed under the weight of the book, this deformation is accompanied by a restoring force upwards. The nature of this restoring force means that an equilibrium is reached between it and the book's weight.
 


MikeyW said:
That is not an example of the 3rd law. The force pairs are:

1. weight of book towards Earth, and weight of Earth towards book
2. contact force on book from table, and contact force on table from book

The weight and contact forces of the book cancel for another reason: the elasticity of the table means that, as it is slightly deformed under the weight of the book, this deformation is accompanied by a restoring force upwards. The nature of this restoring force means that an equilibrium is reached between it and the book's weight.
A very good answer!

AM
 

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