# Newton's Third Law and gravity

• defetey
In summary, according to Newton's 3rd law, the Earth exerts an equal force on a book as the book exerts on the Earth. However, this does not mean that there is a total force of 10 N between them, as the only relevant forces are those acting on the book by you and the Earth. If something were to be placed between them, it would experience a force based on its mass according to Newton's law of gravitation, but the magnitudes would be different from 5 N. There is no 10 N force, as the 5 N forces act on separate bodies.
defetey
This is not really a homework question, just a question I came up with. If the Earth is pulling, for example, a book with a force of 5 N, that means, due to Newton's 3rd law, that the book is also pulling the Earth with a force of 5 N.

Does this mean the total force between them is actually 10 N (since they are each pulling each other with a force of 5 N)? That would imply you would need over 10 N to pick up the book, but I know you only need anything over 5 N. So what am I missing here?

defetey said:
This is not really a homework question, just a question I came up with. If the Earth is pulling, for example, a book with a force of 5 N, that means, due to Newton's 3rd law, that the book is also pulling the Earth with a force of 5 N.

Does this mean the total force between them is actually 10 N (since they are each pulling each other with a force of 5 N)? That would imply you would need over 10 N to pick up the book, but I know you only need anything over 5 N. So what am I missing here?

I believe it is because the only forces being exerted on the book are by you and the earth. Whatever force the book exerts on anything else is irrelevant; the only relevant forces are the ones acting on the book.

But if something was between them, would it experience 10 N of force (5 from the book and 5 from the Earth)?

no it wouldn't ... gravitational force is field force acting on any mass by any mass..
So the thing in between would experience a force based on it mass according to Newtons law of gravitation by both the Earth and the book but their magnitudes would be different(not 5N).

And there's no 10N force ... since 5 acts on the book and 5 on the Earth which are both separate bodies.

I can explain this phenomenon using the principles of Newton's Third Law and gravity. Firstly, Newton's Third Law states that for every action, there is an equal and opposite reaction. In this case, the Earth is exerting a force of 5 N on the book, and the book is exerting a force of 5 N on the Earth in the opposite direction. This means that the forces are equal and opposite, but they act on different objects.

Now, let's consider the force of gravity between the book and the Earth. Gravity is a force that exists between any two objects with mass. The magnitude of this force is determined by the masses of the objects and the distance between them. In this scenario, the Earth has a much larger mass than the book, which means it exerts a greater force of gravity on the book than the book does on the Earth.

So, while the forces are equal and opposite, the force of gravity between the book and the Earth is not. This is why you only need a force greater than 5 N to pick up the book. The extra force is needed to overcome the force of gravity between the book and the Earth.

In summary, while the forces are equal and opposite according to Newton's Third Law, the force of gravity between the book and the Earth is not. Therefore, the total force between them is not 10 N, but rather the amount needed to overcome the force of gravity. I hope this explanation helps to clarify any confusion.

## 1. 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 but opposite force back on the first object.

## 2. How does Newton's Third Law relate to gravity?

Gravity is a force that exists between any two objects with mass. According to Newton's Third Law, when an object with mass exerts a force on another object, the second object will also exert a force back on the first object. In the case of gravity, this means that the Earth exerts a force on an object, and the object also exerts a force back on the Earth.

## 3. Does Newton's Third Law apply to all objects?

Yes, Newton's Third Law applies to all objects, regardless of their mass or size. This is because every object has mass and exerts a force on other objects, according to their masses and the distance between them.

## 4. How does Newton's Third Law explain motion?

Newton's Third Law helps to explain the motion of objects by stating that forces always come in pairs. This means that when one object exerts a force on another object, the second object will also exert a force back on the first object. These forces can cause objects to move, accelerate, or change direction.

## 5. Can Newton's Third Law be observed in everyday life?

Yes, Newton's Third Law can be observed in everyday life. For example, when you walk, your feet exert a force on the ground, and the ground exerts an equal and opposite force back on your feet, allowing you to move forward. Another example is pushing a cart - the force you exert on the cart causes the cart to move, and the cart also exerts a force back on you.

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