What is Newton’s first law?

We explain what is Newton first law or Law of Inertia, its history, formula and examples. In addition, other laws of Newton.

  1. What is Newton first law?

It is known as Newton’s First Law, Newton’s First Law of Motion or Law of Inertia to the first theoretical postulate proposed by the English scientist and mathematician Isaac Newton, around the physical nature of the movement.

Together with the rest of its laws (the second and the third), what is expressed in this first commandment of the physics of movement is part of the fundamental precepts with which Newtonian mechanics or classical mechanics operate. These discoveries revolutionized forever the understanding of matter by scientists around the world.

Newton’s perspective was considered valid, in fact, during the following centuries, until contemporary advances in physics and technology forced us to seek new theories.

Thus, Albert Einstein made studies and contributions that allowed the inauguration of relativistic mechanics. This is distinguished from the Newtonian in that it lacks an absolute reference point, coming to consider magnitudes such as time and space as relative.

Newton’s First Law reads as follows:

Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus illud a viribus impressis cogitur statum suum mutare.

Which in Latin means that:

“Every body continues in its state of rest or uniform rectilinear motion, not far from the printed forces to change its position . 

This means, in simpler terms, that an object always tends to preserve its state – whether at rest or of uniform rectilinear movement – unless some external force acts on it that forces it to change its condition.

  1. Newton’s first law story

Newton's first law physics inertia gravity moon
Newton could explain from the orbit of the Moon to the fall of the objects.

Before Newton, Galileo Galilei had already outlined a first law of inertia , where he indicated that an object has the tendency to preserve its rectilinear and uniform movement unless a force acts on it that forces it to modify its trajectory.

His discovery served as the basis for Newton, who, observing the path in the moon’s sky , deduced that if it did not go off in a straight line following a tangent to its orbit , it is because some other force acted on it to prevent it. This force that prevents it in the celestial case was called gravity .

Newton assumed that the force of gravity acted at a distance, since nothing physically connects the Earth and the Moon. Similarly, when an Olympic ball pitcher spins the instrument on its own axis and finally releases it at once, it moves in some direction along a straight line, but eventually draws a parabola and falls to the ground.

In both cases gravity acts. But in the case of the ball, its trajectory is also affected by the friction with the air in its path (which decreases its speed). That is to say that Galileo’s discoveries allowed Newton to postulate the existence of the force of gravity .

Newton published these and other disquisitions, forming the body of his First and Second Law, in his work Philosophiae naturalis rincipia mathematica (1687), one of the greatest treatises on physics of all time.

  1. Inertia Law Formula

Newton’s law of inertia responds to the following formulation:

Σ F = 0 ↔ dv / dt = 0

It is a vector expression, since the forces are endowed with meaning and guidance. It means that, in the absence of external forces, the speed remains constant over time.

  1. Examples of Newton’s First Law

Newton's first law physics inertia examples
Objects fall in a straight line unless another force modifies their movement.

There are many simple examples of what this law proposes:

  • All objects fall in a straight line , unless the wind and / or the resistance of the air exerts on them (if they are very light) some resistance that modifies their displacement, as occurs with the leaves of the trees.
  • A stone resting on the earth will not move  without an initial force pushing it. And once it moves, it will continue to do so until the friction weakens the initial force, slows it down and stops it.
  • If a surface is polished to reduce its friction force to a minimum, as is the case with waxed floors, the movements will tend to be preserved for much longer unless a greater force stops them.
  1. Newton’s other laws

In his work mentioned above, we also find Newton’s Second Law , also called “Fundamental Principle of Dynamics .” This law attempts to quantify the concept of force : the change of movement of an object is directly proportional to the driving force printed on it and will occur according to the straight line according to which said force is executed.

The third law of Newton is known as the principle of action and reaction , since it states that for every force exerted on an object there is an opposite, that is, but in the opposite direction such that the object exerts on who plays. That is to say, that every action accompanies an equal but opposite reaction.

Unlike the first two, the third law of movement is entirely original from Newton , without previous versions of Galileo, Hooke or Huygens.

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