# Newton’s fourth law of motion | Newton’s 4th law

Newton’s laws have brought the revaluation in Physics in 19th century. These laws have important roles in science. But, how many laws does Newton have? The answer is that Sir Isaac Newton introduced many laws in many branches of science. Here, we are interested in laws of motion only. We already have discussed three laws of motion given by him. Is there any Newton’s fourth law of motion? Is the law of Gravitation his fourth law of motion?

Yes, there is Newton’s 4th law which is unknown to most of the students. But, gravitational law is not the fourth law of motion. In this article, we are going to discuss what is Newton’s fourth law of motion? What is its mathematical form?

Newton’s laws of motion:

1. Newton’s first law of motion or the law of inertia
2. Second law of motion for force and acceleration
3. Newton’s third law of action and reaction.

But, there is another untold law of motion. This law is known as Newton’s 4th law.

## Newton’s fourth law of motion

Newton’s fourth law of motion is related to the nature and calculation of forces. This law states that the forces are vector quantities and they obey the principle of superposition during their vector addition.

## Facts of Fourth law of Newton

1. Newton did not state his fourth law of motion. He has never mentioned this law. People assumed this law.
2. Some people think that the law of universal gravitation is Newton’s fourth law. But again, Newton did not mention this during the statement of this law or at any time. People renamed the gravitation law as the fourth law of Newton on the basis of counting the number of laws given by sir Isaac Newton. So, Newton’s law of gravitation is not Newton’s fourth law of motion.
3. It is better to accept that there are only three laws of motion and the law of universal gravitation is different from those. Newton’s second law of motion is applied in the law of gravitation during calculating the gravitational force between two objects.
4. All the vector addition of force acting on a system are examples of Newton’s fourth law.

## Formula of Newton’s fourth law of motion

Clearly, there is no fourth law of motion. Hence, there is no established formula for Newton’s fourth law. However, one can write the formula of fourth law of motion just like the principle of superposition.

If $\small \vec{F_{1}}$, $\small \vec{F_{2}}$, $\small \vec{F_{2}}$, ……….. are the forces acting on any system, then the net force acting on the system is, $\small {\color{Blue} \vec{F}= \vec{F_{1}}+\vec{F_{2}}+\vec{F_{3}}+…}$.

This is the equation of Newton’s 4th law in vector form.

1. What is Newton’s fourth law of motion?
2. Is the law of gravitation the fourth law of Newton?
3. Newton’s 4th law
4. Newtons 4th law

So, how many laws of motion are there? comment the answer.

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