# dynamic

2022

We explain what dynamics is and what are the fundamental laws of dynamics. History of discovery, and related principles.

Isaac Newton established the fundamental laws of dynamics.

## What is Dynamics?

Dynamics is the part of the physical that studies the relationship between forces that act on a body and the effects that will occur on the movement of that body.

Ancient Greek thinkers believed that the speed and constancy of motion in a body's straight line (a phenomenon described years later as uniform rectilinear motion or MRU) were proportionally related to a constant force. By extension, the fall of a body was believed to belong to that category, so it was assumed that the body that weighed the most would fall faster.

Later, Galileo Galilei understood that the fall of the bodies could not be a uniform movement, and that from the same height, two bodies of different weight take the same time to fall. This context was what made it possible for Isaac Newton to establish the three fundamental laws of dynamics, which explained the fundamental patterns of the behavior of bodies.

## Newton's laws

When a body is at rest, the forces applied to it have zero resultant.
• The principle of inertia. It indicates that when a body is at rest, or describes a movement with the characteristics of MRU, the forces applied to it have a null resultant. You have to be very careful in this case, since they influence, for example, the friction force. When the forces are balanced, the MRU can really take place.
• Force equals mass by acceleration. This is the fundamental formula of dynamics, and it comes from assuming a body at rest on a horizontal surface, which is subject to a force parallel to that surface, being able to dispense with friction: we will see that the body moves at a acceleration constant. If another force of greater intensity is applied to it, the acceleration will vary proportionally.
In this way we arrive at this formula, and we can establish the international unit of force, the Newton (N), defined as the force that drives a mass of one kilogram with an acceleration of one meter per second squared.
• Law of action and reaction. Whenever a body exerts a force on another, this second exerts a contrary of equal intensity and address but opposite sense on the first. The first example is that of a body that weighs on a surface, which will receive from that the action of a force that opposes the attraction that the earth exerts on it.

These laws are the fundamental laws of dynamics, which apply fundamentally to uniform rectilinear motion. However, there is also a dynamics of circular motion, which happens when the force applied to a body can be maintained constantly in modulus, perpendicular to the direction of movement. This occurs, for example, in the case of the constant attractive force of the Sun over a planet, which prevents it from exerting a rectilinear motion instead of the orbit.

However, there is also the analysis of the behavior of bodies when various particles, in addition to the aforementioned forces. The part of physics you use methods statistics to study the global behavior of systems is the thermodynamics.

It has a series of principles, among which can be mentioned the thermal equilibrium, that is, the equality between the heat received and that emitted by the body, achieved through the exchange of heat. It is also said that energy is not produced or destroyed, but is transformed, making it impossible to produce work without the consumption of Energy, and from this it arises that heat cannot be totally transformed into work, there is always a loss.

There is also a colloquial use of the term, which is applied to speak symbolically of things that are in motion. You can talk about the dynamics of processes politicians, public events or anything, to refer to 'how it developed' for a period of weather. Also, it is used as adjective to talk about people who are very restless and who spend much of their time moving.

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