What is kinematics?

We explain what is the kinematics and what is the origin of this branch of physics. Elements of kinematics, and examples of application.

1. What is kinematics?

Kinematics is a branch of physics that studies the movement of solid objects and their trajectory as a function of time , without taking into account the origin of the forces that motivate it. For this, the speed ( displacement between time used) and acceleration (change in speed between time used) of the moving object is taken into account.

The origins of kinematics date back to ancient astronomy , when astronomers and philosophers such as Galileo Galilei watched the movement of spheres on inclined planes and in free fall to understand the movement of the celestial stars. These studies, together with those of Nicolás Copernicus, Tycho Brahe and Johannes Kepler served as reference to Isaac Newton to formulate his three Laws of the movement, and all this jointly founded, already at the beginning of the 18th century, modern kinematics.

The contributions of the French Jean Le Rond d’Alembert, Leonhard Euler and André-Marie Ampère were key in the establishment of this discipline , baptized by Ampère himself as kinematics (from the Greek kinéin , to move, to move).

The much later postulation of relativity by Albert Einstein would turn the discipline around and found relativistic kinematics, in which time and space are not absolute dimensions, as is the speed of light.

2. Elements of the kinematics

The basic elements of kinematics are three: space, time and a mobile . We must bear in mind that in classical mechanics the first two, time and space, are absolute dimensions, independent of the mobile and prior to its existence, as well as of all observable physical phenomena .

Space, thus, is represented by a Euclidean space. Time is considered unique in any region of the universe , and a mobile can be any body in motion . In fact, the simplest mobiles are particles (and their study opens the field of particle kinematics), but more often it is considered a rigid solid (analogous to a particle system).

In that sense, classical kinematics contemplates the following types of movement:

• Uniform rectilinear movement . A body travels at a stable speed V, with acceleration 0 all the time, in a straight line.
• Uniformly accelerated rectilinear movement . A body moves at a speed that varies linearly, since its acceleration is constant, as time progresses.
• SHM . It is a periodic reciprocating movement, in which a body oscillates around a point of equilibrium in a certain direction and in regular units of time.
• Parabolic movement . This is the composition of two different rectilinear movements: one horizontal and constant speed, and another vertical and uniformly accelerated.
• Uniform circular motion . As the name implies, it is the movement that draws perfect circles in its path, maintaining its speed in invariable time.
• Uniformly accelerated circular movement . It is the same as the uniformly accelerated rectilinear, only in circles.
• Complex harmonic motion . It is the combinatorial result of various simple harmonic movements, in different directions.

3. Kinematics Examples

Most of the known movements on the face of the earth are good examples of kinematics studies. The fall of a body , for example, is a motion uniformly accelerated by the force of gravity , which prints its weight downward.

Another possible example is a body suspended from an elastic , such as a spring, whose movement will be simple or complex harmonic depending on the forces we exert on it.

Finally, the movement of the hands of the clock or of a loose object inside a centrifuge (the clothes in the washing machine, perhaps), allows to illustrate the uniform or accelerated circular movement.