# Third Newtonian law most fundamental

• flashgordon2!
In summary: Each law is precise enough to describe a particular kind of behavior, but they are all incomplete in the sense that they don't describe everything.
flashgordon2!
third law is equal and opposite reaction . . . the first law is inertia of mass.

From everything I can remember reading, people often talk about the mystery of inertia in bodies . . . well, i finally got around to thinking about this stuff(admittedly), and it seems to me that the first law is a derivable from the third. If you try to pull a set of particles all reacting to your pull(and maybe some initial pushing of contacting a body of particles), then, all those particles will push away(and do some back and forth reactions amongst themselves) . . . so, the first law is explainable by the third.

I've never heard anybody say this, so, sorry is somebody has!

Nope, there are three laws.

Ok, so, really Newton's first law reads:

If a body is subjected to no net force, it receives no net acceleration.

For every force of "A" on "B", there is an equal and opposite force of "B" on "A"

So I don't see how you derive N1L from N3L.

ZM

Last edited:
If you pull at a set of particles, why would they pull away from you unless there was another force acting on them?

In classical electrodynamics we have N1L is true, and N3L is false. This doesn't, however, contradict what you are saying.

Note that Newton's First law is not true for all observers. It is only true for an observed fixed in some inertial frame. Think of the first law as defining the concept of an inertial frame.

The first law only vaguely mentions forces. The second law expounds on this concept, describing what an observer tied to an inertial frame sees when a force is appied to some object. The second law defines force in terms of behavior in an inertial frame. The third law further expands on the concept of force, saying that forces come in equal and opposite pairs.

One cannot start with the third law as the most fundamental because it depends on the concept of a force", defined in the second law. Similarly, the second law depends on the concept of an inertial frame, defined in the first law. Newton was no dummy. He established these laws in the order he did on intentionally.

Also worth noting, is that the first law defining an inertial frame requires that you know how forces act in an inertial frame, which in turn requires the second and third laws. None of Newton's laws are independent, but at the same time they're very vague in the sense of "what exactly is a force?". However, you answer that question by knowing what's acting on what and how.

StatMechGuy said:
but at the same time they're very vague in the sense of "what exactly is a force?"..

Not at all. It is as precise as "points, lines and planes" are in Hilbert's axiomatization of geometry.

## 1. What is the Third Newtonian Law?

The Third Newtonian Law, 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 and opposite force back on the first object.

## 2. Why is the Third Newtonian Law considered the most fundamental?

The Third Newtonian Law is considered the most fundamental because it is the foundation for understanding all other laws of motion. It explains how forces interact with each other and how objects move in response to these forces.

## 3. Can the Third Newtonian Law be applied to all types of forces?

Yes, the Third Newtonian Law can be applied to all types of forces, including gravitational, electromagnetic, and nuclear forces. It is a universal law that governs the interactions between all objects in the universe.

## 4. How does the Third Newtonian Law relate to conservation of momentum?

The Third Newtonian Law is closely related to the law of conservation of momentum. According to this law, the total momentum of a system remains constant, meaning that the total force exerted on a system is always equal to the total force exerted back on it. This is a direct result of the Third Newtonian Law.

## 5. What are some real-life examples of the Third Newtonian Law?

There are many real-life examples of the Third Newtonian Law, such as pushing against a wall, where the wall exerts an equal and opposite force back on you. Another example is the recoil of a gun when fired, where the bullet exerts a force forward, and the gun experiences an equal force in the opposite direction.

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