# Newton’s Laws of Motion, What is it? Definition, Formula, Examples.,

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The Newton’s laws of motion(NLM), may seem obvious to us today, centuries ago they were considered revolutionary. The three laws of motion help us understand how objects behave when they are standing still, when moving and when forces act upon them. This article is a description of Sir Isaac Newton’s Laws of motion and a summary of what they mean.

### History

Newton’s laws first appeared in his masterpiece, Philosophiae Naturalis Principia Mathematica (1687), commonly known as the Principia. In 1543 Nicolaus Copernicus suggested that the Sun, rather than Earth, might be at the centre of the universe. In the intervening years Galileo, Johannes Kepler, and Descartes laid the foundations of a new science that would both replace the Aristotelian worldview, inherited from the ancient Greeks, and explain the workings of a heliocentric universe. In the Principia Newton created that new science. He developed his three laws in order to explain why the orbits of the planets are ellipses rather than circles, at which he succeeded, but it turned out that he explained much more. The series of events from Copernicus to Newton is known collectively as the Scientific Revolution.

In the 20th century Newton’s laws were replaced by quantum mechanics and relativity as the most fundamental laws of physics. Nevertheless, Newton’s laws continue to give an accurate account of nature, except for very small bodies such as electrons or for bodies moving close to the speed of light. Quantum mechanics and relativity reduce to Newton’s laws for larger bodies or for bodies moving more slowly.

### 1. Newton’s First Law of Motion

The first law of motion implies that things cannot start, stop, or change direction all by themselves. It requires some force from the outside to cause such a change. This property of massive bodies to resist changes in their state of motion is called inertia. Newton’s first law is also known as the law of inertia.

Newton’s 1st law states that a body at rest or uniform motion will continue to be at rest or uniform motion until and unless a net external force acts on it.

The crucial point here is that if there is no net force resulting from unbalanced forces acting on an object, then the object will maintain a constant velocity. If that velocity is zero, then the object remains at rest. And if an additional external force is applied, the velocity will change because of the force.

### 2. Newton’s Second Law of Motion

The second law of motion describes what happens to the massive body when acted upon by an external force. The 2nd law of motion states that the force acting on the body is equal to the product of its mass and acceleration.

Newton’s 2nd law states that the acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

Newton’s second law describes precisely how much an object will accelerate for a given net force.

Mathematically, we express the second law of motion as follows:

f∝dPdt

⇒f∝mv−mut

⇒f∝m(v−u)t

⇒f∝ma

⇒f=kma

In the equation, k is the constant of proportionality, and it is equal to 1 when the values are taken in SI unit. Hence, the final expression will be,

F=ma

### 3. Newton’s Second Law of Motion

The third law of motion describes what happens to the body when it exerts a force on another body.

The Newton’s 3rd law states that for every action there is an equal and opposite reaction.

When two bodies interact, they apply force on each other that are equal in magnitude and opposite in direction. To understand Newton’s third law with the help of an example, let us consider a book resting on a table. The book applies a downward force equal to its weight on the table.

According to the third law of motion, the table applies an equal and opposite force on the book. This force occurs because the book slightly deforms the table; as a result, the table pushes back on the book like a coiled spring. Newton’s third law of motion implies the conservation of momentum.

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