Newton’s Laws

What are Newton’s Laws?

The Newton’s laws are three principles that serve to describe the movement of bodies, based on an inertial reference system (real forces with constant speed).

Newton’s three laws are:

  • First law or law of inertia.
  • Second law or fundamental law of dynamics.
  • Third law or principle of action and reaction.

These laws that relate the force, speed and movement of bodies are the basis of classical mechanics and physics. They were postulated by the English physicist and mathematician Isaac Newton, in 1687.

Newton’s first law: law of inertia

Newton's laws, law of inertia

The law of inertia or first law states that a body will remain at rest or in straight motion with a constant speed, unless an external force is applied.

In other words, it is not possible for a body to change its initial state (either at rest or in motion) unless one or more forces intervene.

The formula for Newton’s first law is:

sum of white space for white space of F equal to 0 mushroom for left and right numerator dv over denominator dt end of fraction equal to 0

If the sum of the forces (Σ F) applied to a body is equal to zero, then the change in its velocity with respect to time (dv/dt) will also be equal to zero.

An example of Newton’s first law is a ball at rest. In order for it to move, it requires a person to kick it (external force); otherwise, it will remain at rest.

On the other hand, once the ball is in motion, ignoring friction with the ground, another force must also intervene for it to stop and return to its state of rest.

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Although this is the first of the laws of motion proposed by Newton, this principle had already been postulated by Galileo Galilei in the past. For this reason, Newton alone is credited with publishing the law, and Galilei is credited as the original author.

See also: Physics.

Newton’s second law: fundamental law of dynamics

Newton's laws, law of dynamics

The fundamental law of dynamics, Newton’s second law or fundamental law, states that the net force that is applied to a body is proportional to the acceleration that it acquires in its trajectory.

The formula for Newton’s second law is:

F you still love a.  espaço acceleration or n equal to m.  space to


F = net force
m = mass, expressed in Kg.
a = acceleration, expressed in m/stwo (meter per second squared).

See also Dynamics.

Newton’s third law: principle of action and reaction

Newton's laws, law of action and reaction

Newton’s third law postulate says that every action generates an equal reaction, but in the opposite direction.

The formula for the law of action and reaction is:

F com 1 seta para a direct 2 subscribed fim do subscribed equal to F com 2 seta para a direct 1 subscribed fim do subscribed

The force of body 1 on body 2 (F1-2)or action force, is equal to the force of body 2 on body 1 (F2-1) , or reaction force. The reaction force will have the same direction and magnitude as the action force, but opposite to it.

An example of Newton’s third law it is when we have to move a sofa, or any heavy object. The action force applied on the object causes it to move, but at the same time it generates a reaction force in the opposite direction that we perceive as resistance from the object.

See also Types of movement.

law of universal gravitation

Newton's laws, universal law of attraction

The postulate of this law of physics states that the force of attraction of two bodies is proportional to the product of their masses.

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The intensity of that attraction will be stronger the closer and more massive the bodies are.

The formula for the law of universal gravitation is:

F equal to numerator G times m 1 times m 2 over denominator d ao quadrado fim da fração

The force exerted between the two bodies with mass (F) is equal to the universal gravitational constant (G) times the product of the two masses involved (m1.m2) divided by the distance that separates them, squared (dtwo).

An example of the law of gravitation we have it in the gravitational attraction exerted by two balls of bowling. The closer they are to each other, the greater the force of attraction.

See also:

  • Second law of Newton
  • Gravity
  • what is inertia
  • Branches of physics


Sears, FW, Zemansky, MW, Young, HD Freedman, RA (2009). University Physics vol.1. 12th ed. PearsonEducation. Mexico.

Sebastian, JSM (2013). Newton’s Laws of Mechanics: A Historical Review and its Implications for Teaching Texts. Didactics of experimental and social sciences 27:199-217