Reaction force of book resting on table.

[SaintJude]

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Kaplan is attempting to teach me Newton's 3rd law.

A book is resting on a table. What is the reaction force to the weight of the book?

A: "It's not the normal force! It is the force on the earth due to the book. The normal force happens to equal the weight of the book, because the force isn't accelerating. "

Can someone please explain the rationale behind this sentence ?

 

[Ssina]

well you know that the 3rd Newt forces are acting on different objects!
weight of the book is the force of the earth gravity on the book, and it's Newt 3rd force (or reaction force) would be book pulling the earth toward itself... forces of equal magnitudes on different objects!

normal force, is the force of the surface that is applied to the book so the book doesn't go through the surface of the table/earth... so it's acting on the book just like the weight so they can't be action/reaction force.

 

[MedPR]

Kaplan is attempting to teach me Newton's 3rd law.

A book is resting on a table. What is the reaction force to the weight of the book?

A: "It's not the normal force! It is the force on the earth due to the book. The normal force happens to equal the weight of the book, because the force isn't accelerating. "

Can someone please explain the rationale behind this sentence ?

Weight of the book is mass and earth's gravity. The reaction force must be a force on whatever is exerting a force on the book (equal and opposite). The table isn't the thing giving the book weight, the earth is. Therefore, the reaction force of the weight must be a force on the earth.. Which is the weight of the book.

 

[chiddler]

Kaplan is attempting to teach me Newton's 3rd law.

A book is resting on a table. What is the reaction force to the weight of the book?

A: "It's not the normal force! It is the force on the earth due to the book. The normal force happens to equal the weight of the book, because the force isn't accelerating. "

Can someone please explain the rationale behind this sentence ?

Suppose you push a box on the ceiling and move it forward. What is normal force? Not mg, right? It depends on how hard you push up!