Why Does a Book on a Table Stay at Rest Despite Action and Reaction Forces?

In summary, the book lying at rest on a table is in equilibrium because the gravitational force and the upward normal reaction force of the table are equal and opposite. However, these two forces are not 3rd law pairs (action/reaction pairs). The 3rd law pairs to these forces are the gravitational force exerted on the earth by the book and the force exerted on the table by the book. Therefore, the book is in equilibrium because the forces acting on it add up to zero, but they are not action and reaction pairs.
  • #1
moatasim23
78
0
Action and reaction do not balance each other.But then why a book lying on a table lies at rest?The reaction force and the gravitational force cannot balance each other.Then how is it?
 
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  • #2
moatasim23 said:
Action and reaction do not balance each other.But then why a book lying on a table lies at rest?The reaction force and the gravitational force cannot balance each other.Then how is it?
Action and reaction forces act on different bodies, so they don't 'balance'. The book is in equilibrium because the forces acting on the book add up to zero (they 'balance'). But those forces are not action/reaction pairs.

The first thing you need to do is identify all the forces acting on the book and their third law pairs.
 
  • #3
Doc Al said:
Action and reaction forces act on different bodies, so they don't 'balance'. The book is in equilibrium because the forces acting on the book add up to zero (they 'balance'). But those forces are not action/reaction pairs.

The first thing you need to do is identify all the forces acting on the book and their third law pairs.

Can u help me to identify them?I can only think of two forces.
THANKS.
 
  • #4
moatasim23 said:
Can u help me to identify them?I can only think of two forces.
OK, what are those two forces? And what bodies exert those forces? (That will help you identify the 3rd law pairs.)
 
  • #5
hi moatasim23! :smile:

sorry, but i don't understand any of your post :confused:
moatasim23 said:
Action and reaction do not balance each other.

action and reaction are always equal and opposite
But then why a book lying on a table lies at rest?The reaction force and the gravitational force cannot balance each other.

they do balance each other

what makes you think that they don't? :confused:
 
  • #6
Doc Al said:
OK, what are those two forces? And what bodies exert those forces? (That will help you identify the 3rd law pairs.)

Gravitational force and the upward normal reaction force of the table.
 
  • #7
moatasim23 said:
Gravitational force and the upward normal reaction force of the table.
Good. Those two forces happen to be equal and opposite, thus the book is in equilibrium. But those two forces are not 3rd law pairs (action/reaction pairs).

The gravitational force on the book is exerted by the earth. The 3rd law pair to that force is an equal and opposite gravitational force exerted on the earth by the book. (They attract each other.)

The upward force of the table on the book is exerted by the table. The 3rd law pair to that force is an equal and opposite force exerted on the table by the book. (They push against each other.)
 
  • #8
Thanks DOC AL.This question was confusing me for a lot time.Thanks a lot.
 

What is Newton's Third Law of Motion?

The Third Law of Motion, also known as the Law of Action and Reaction, states that for every action, there is an equal and opposite reaction. This means that when an object exerts a force on another object, the second object will exert an equal force in the opposite direction.

What are some examples of Newton's Third Law of Motion?

Some examples of Newton's Third Law of Motion include a rocket launching off the ground, a person pushing a shopping cart, and a ball bouncing off a wall. In each of these situations, there is an action and a reaction force that are equal and opposite.

How does Newton's Third Law of Motion apply to everyday life?

Newton's Third Law of Motion applies to everyday life in many ways. For example, when you walk, your feet push against the ground, and the ground pushes back with an equal force, allowing you to move forward. When you sit on a chair, your weight exerts a downward force on the chair, and the chair exerts an equal upward force, keeping you from falling through.

Does Newton's Third Law of Motion only apply to objects in motion?

No, Newton's Third Law of Motion applies to all objects, whether they are in motion or at rest. Even if an object is not moving, it still has potential energy, and the forces acting on it follow the Third Law of Motion.

How does Newton's Third Law of Motion relate to the other Laws of Motion?

The Laws of Motion, including the Third Law, work together to describe the motion of objects. The First Law states that objects will remain at rest or in motion at a constant speed unless acted upon by a force. The Second Law relates the force applied to an object to its acceleration. And the Third Law explains the relationship between forces acting on different objects.

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