Almost all the physics students know the Newton’s three laws of motion. But the fourth law of motion is still unknown to many of the students. Here I am going to discuss what is Newton’s fourth law of motion? This is a hidden law of Newton.

We already have discussed –

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

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

**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**

- Newton did not state his fourth law of motion. He has never mentioned this law. People assumed this law.
- Some people think that
**the law of universal gravitation**is the 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, the Newton’s law of gravitation is not the Newton’s fourth law of motion. - 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. - All the vector addition of force acting on a system are the 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 fourth law.

**People also ask:**

**What is Newton’s fourth law of motion?****Is the law of gravitation the fourth law of Newton?**

This is all from this article. If you have any doubt on this topic you can ask me in the comment section.

Thank You!

**Related Posts:**

**First law of motion****Second law of motion****Law of Gravitation**

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