Reaction force on a book resting on top of a table.

[ysk1]

Question:

A book is resting on top of a table.

1. Do the downward force of gravity and the upward force of normal force constitute a 3rd law pair? (Yes/No)

2. The reaction to the force of gravity is exerted on the (earth/table/book) by the (earth/table/book). Its direction is (upward/downward).





According to Newton's third law, I know that reaction force occurs when object A receiving an impact from object B exerts a force equal in magnitute but opposite in direction to object B.
But how do you show this on free body diagram?



Thank you.

 

[Nate810]

Answer 1: YesAnswer 2: The reaction to the force of gravity is exerted on the table by the book. Its direction is upward.

 

[kyle8921]

1. Yes, the downward force of gravity and the upward force of normal force constitute a third law pair. According to Newton's third law, for every action, there is an equal and opposite reaction. In this case, the action is the book's weight pulling down on the table, and the reaction is the table pushing up on the book with an equal force. This is known as the normal force.

2. The reaction to the force of gravity is exerted on the earth by the book. Its direction is upward. This means that the book is pushing down on the table with its weight, and the table is pushing up on the book with an equal force. The reaction force to this downward force is exerted on the earth, as the earth is supporting the weight of the book and the table. The direction of this reaction force is upward, as it is opposing the downward force of gravity on the book. This can be shown on a free body diagram by drawing an arrow pointing upward labeled as the normal force, and another arrow pointing downward labeled as the weight of the book. The two arrows should be equal in length, indicating that the forces are balanced.