THE 13 BRANCHES OF CLASSICAL AND MODERN PHYSICS - PHYSICAL - 2025

Among the branches of classical and modern physics we can highlight acoustics, optics or mechanics in the most primitive field, and cosmology, quantum mechanics or relativity in those of more recent application.

Classical physics describes theories developed before 1900, and modern physics the events that occurred after 1900. Classical physics deals with matter and energy, on a macro-scale, without going deep into the more complex studies of quantums. of modern physics.

Max Planck, one of the most important scientists in history, marked the end of classical physics and the beginning of modern physics with quantum mechanics.

Branches of classical physics

1- Acoustics

The ear is the biological instrument par excellence to receive certain wave vibrations and interpret them as sound.

Acoustics, which deals with the study of sound (mechanical waves in gases, liquids and solids), is related to the production, control, transmission, reception and effects of sound.

Acoustic technology includes music, the study of geological, atmospheric and underwater phenomena.

Psychoacoustics studies the physical effects of sound on biological systems, present since Pythagoras heard, for the first time, the sounds of vibrating strings and hammers hitting anvils in the 6th century BC. But the most shocking development in medicine is ultrasound technology.

2- Electricity and Magnetism

Electricity and magnetism come from a single electromagnetic force. Electromagnetism is a branch of physical science that describes the interactions of electricity and magnetism.

The magnetic field is created by a moving electric current and a magnetic field can induce the movement of charges (electric current). The rules of electromagnetism also explain geomagnetic and electromagnetic phenomena, describing how charged particles of atoms interact.

Formerly, electromagnetism was experienced on the basis of the effects of lightning and electromagnetic radiation as a light effect.

Magnetism has long been used as a fundamental instrument for compass-guided navigation.

The phenomenon of electric charges at rest was detected by the ancient Romans, who observed the way in which a rubbed comb attracted particles. In the context of positive and negative charges, like charges repel, and different charges attract.

You may be interested in knowing more about this topic by discovering the 8 types of electromagnetic waves and their characteristics.

3- Mechanics

It is related to the behavior of physical bodies, when they are subjected to forces or displacements, and the subsequent effects of the bodies in their environment.

At the dawn of modernism, scientists Jayam, Galileo, Kepler, and Newton laid the groundwork for what is now known as classical mechanics.

This sub-discipline deals with the movement of forces on objects and particles that are at rest or moving at speeds significantly slower than that of light. Mechanics describes the nature of bodies.

The term body includes particles, projectiles, spaceships, stars, parts of machinery, parts of solids, parts of fluids (gases and liquids). Particles are bodies with little internal structure, treated as mathematical points in classical mechanics.

Rigid bodies have size and shape, but retain a simplicity close to that of the particle and can be semi-rigid (elastic, fluid).

4- Fluid mechanics

Fluid mechanics describes the flow of liquids and gases. Fluid dynamics is the branch from which sub-disciplines such as aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion) emerge.

Fluid dynamics is widely applied: for the calculation of forces and moments in airplanes, the determination of the mass of the petroleum fluid through the pipelines, in addition to the prediction of weather patterns, the compression of nebulae in the interstellar space and nuclear weapons fission modeling.

This branch offers a systematic structure that encompasses empirical and semi-empirical laws derived from flow measurement and used to solve practical problems.

The solution to a fluid dynamics problem involves calculating fluid properties, such as flow velocity, pressure, density, and temperature, and functions of space and time.

5- Optics

Optics deals with the properties and phenomena of visible and invisible light and vision. Study the behavior and properties of light, including its interactions with matter, in addition to building appropriate instruments.

Describes the behavior of visible, ultraviolet, and infrared light. Since light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves have similar properties.

This branch is relevant for many related disciplines such as astronomy, engineering, photography and medicine (ophthalmology and optometry). Its practical applications are found in a variety of everyday objects and technologies, including mirrors, lenses, telescopes, microscopes, lasers, and fiber optics.

6- Thermodynamics

Branch of physics that studies the effects of work, heat, and energy in a system. It was born in the 19th century with the appearance of the steam engine. It deals only with the large-scale observation and response of an observable and measurable system.

Small-scale gas interactions are described by the kinetic theory of gases. The methods complement each other and are explained in terms of thermodynamics or by kinetic theory.

The laws of thermodynamics are:

• Enthalpy Law: Relates the various forms of kinetic and potential energy, in a system, with the work that the system can do, plus the transfer of heat.
• This leads to the second law, and to the definition of another state variable called the entropy law.
• The zeroth law defines large-scale thermodynamic equilibrium, of temperature as opposed to the small-scale definition related to the kinetic energy of molecules.

Branches of modern physics

7- Cosmology

It is the study of the structures and dynamics of the Universe on a larger scale. Investigate its origin, structure, evolution and final destination.

Cosmology, as a science, originated with the Copernicus principle - celestial bodies obey physical laws identical to those of the Earth - and Newtonian mechanics, which allowed us to understand these physical laws.

Physical cosmology began in 1915 with the development of Einstein's general theory of relativity, followed by great observational discoveries in the 1920s.

Dramatic advances in observational cosmology since the 1990s, including the cosmic microwave background, distant supernovae, and redshift uprisings of the galaxy, led to the development of a standard model of cosmology.

This model adheres to the content of large amounts of dark matter and dark energies contained in the universe, whose nature is not yet well defined.

8- Quantum Mechanics

Branch of physics that studies the behavior of matter and light, on the atomic and subatomic scale. Its objective is to describe and explain the properties of molecules and atoms and their components: electrons, protons, neutrons and other more esoteric particles such as quarks and gluons.

These properties include the interactions of the particles with each other and with electromagnetic radiation (light, X-rays, and gamma rays).

Multiple scientists contributed to the establishment of three revolutionary principles that gradually gained acceptance and experimental verification between 1900 and 1930.

• Quantified properties. Position, speed, and color can sometimes only occur in specific amounts (like clicking number by number). This is in contrast to the concept of classical mechanics, which says that such properties must exist on a flat, continuous spectrum. To describe the idea that some properties click, scientists coined the verb quantify.
• Light particles. The scientists refuted 200 years of experiments by postulating that light can behave like a particle and not always "like waves / waves in a lake."
• Waves of matter. Matter can also behave like a wave. This is demonstrated by 30 years of experiments that affirm that matter (such as electrons) can exist as particles.

9- Relativity

This theory encompasses two theories of Albert Einstein: special relativity, which applies to elementary particles and their interactions –describing all physical phenomena except gravity- and general relativity which explains the law of gravitation and its relationship with other forces of nature.

It applies to the cosmological, astrophysical, and astronomy realm. Relativity transformed the postulates of physics and astronomy in the 20th century, banishing 200 years of Newtonian theory.

He introduced concepts such as spacetime as a unified entity, simultaneity relativity, kinematic and gravitational dilation of time, and longitude contraction.

In the field of physics, he improved the science of elementary particles and their fundamental interactions, along with the inauguration of the nuclear age.

Cosmology and astrophysics predicted extraordinary astronomical phenomena such as neutron stars, black holes, and gravitational waves.

10-Nuclear physics

It is a field of physics that studies the atomic nucleus, its interactions with other atoms and particles, and its constituents.

11-Biophysics

Formally, it is a branch of biology, although it is closely related to physics, since it studies biology with physical principles and methods.

12-Astrophysics

Formally, it is a branch of astronomy, although closely related to physics, as it studies the physics of the stars, their composition, evolution and structure.

13-Geophysics

It is a branch of geography, although it is closely related to physics, since it studies the Earth with the methods and principles of physics.

Research examples from each branch

1- Acoustics: UNAM research

The acoustics laboratory of the Department of Physics of the Faculty of Sciences of the UNAM conducts specialized research in the development and implementation of techniques that allow studying acoustic phenomena.

The most common experiments include different media with dissimilar physical structures. These media can be fluids, wind tunnels, or the use of a supersonic jet.

An investigation that is currently taking place at UNAM is the frequency spectrum of a guitar, depending on where it is struck. The acoustic signals emitted by dolphins are also being studied (Forgach, 2017).

2- Electricity and magnetism: effect of magnetic fields in biological systems

The Francisco José Caldas District University conducts research on the effect of magnetic fields on biological systems. All this in order to identify all the previous research that has been done on the subject and to issue new knowledge.

Research indicates that the Earth's magnetic field is permanent and dynamic, with alternating periods of both high and low intensity.

They also speak of the species that depend on the configuration of this magnetic field to orient themselves, such as bees, ants, salmon, whales, sharks, dolphins, butterflies, turtles, among others (Fuentes, 2004).

3- Mechanics: human body and zero gravity

For more than 50 years, NASA has conducted research on the effects of zero gravity on the human body.

These investigations have allowed many astronauts to move safely on the Moon, or live for more than a year on the International Space Station.

NASA research analyzes the mechanical effects that zero gravity has on the body, with the aim of reducing them and ensuring that astronauts can be sent to more remote places in the solar system (Strickland & Crane, 2016).

4- Fluid mechanics: Leidenfrost effect

The Leidenfrost effect is a phenomenon that takes place when a drop of a fluid touches a hot surface, at a temperature higher than its boiling point.

Doctoral students at the University of Liège created an experiment to find out the effects of gravity on the evaporation time of a fluid, and its behavior during this process.

The surface was initially heated and sloped when necessary. The water droplets used were tracked by means of infrared light, activating servo motors every time they moved away from the center of the surface (Research and Science, 2015).

5- Optics: Ritter's observations

Johann Wilhelm Ritter was a German pharmacist and scientist, who conducted numerous medical and scientific experiments. Among his most notable contributions to the field of optics is the discovery of ultraviolet light.

Ritter based his research on the discovery of infrared light by William Herschel in 1800, thus determining that the existence of invisible lights was possible and conducting experiments with silver chloride and different light beams (Cool Cosmos, 2017).

6- Thermodynamics: thermodynamic solar energy in Latin America

This research focuses on the study of alternative sources of energy and heat, such as solar energy, having as main interest the thermodynamic projection of solar energy as a sustainable energy source (Bernardelli, 201).

For this purpose, the study document is divided into five categories:

1- Solar radiation and energy distribution on the earth's surface.

2- Uses of solar energy.

3- Background and evolution of the uses of solar energy.

4- Thermodynamic installations and types.

5- Case studies in Brazil, Chile and Mexico.

7- Cosmology: Dark Energy Survey

The Survey on Dark Energy or Dark Energy Survey, was a scientific study carried out in 2015, whose main purpose was to measure the large-scale structure of the universe.

With this investigation, the spectrum was opened to numerous cosmological inquiries, which seek to determine the amount of dark matter present in the current universe and its distribution.

On the other hand, the results produced by DES contradict the traditional theories about the cosmos, issued after the Planck space mission, financed by the European Space Agency.

This research confirmed the theory that the universe is currently composed of 26% dark matter.

Positioning maps were also developed that precisely measured the structure of 26 million distant galaxies (Bernardo, 2017).

8- Quantum mechanics: information theory and quantum computing

This research seeks to investigate two new areas of science, such as information and quantum computing. Both theories are fundamental to the advancement of telecommunications and information processing devices.

This study presents the current state of quantum computing, supported by the advances made by the Group of Quantum Computation (GQC) (López), an institution dedicated to giving talks and generating knowledge on the subject, based on the first Turing's postulates on computing.

9- Relativity: Icarus experiment

The Icarus experimental research, carried out in the laboratory of Gran Sasso, Italy, brought reassurance to the scientific world by verifying that Einstein's theory of relativity is true.

This research measured the speed of seven neutrinos with a light beam provided by the European Center for Nuclear Research (CERN), concluding that neutrinos do not exceed the speed of light, as had been concluded in past experiments from the same laboratory.

These results were the opposite of those obtained in previous experiments by CERN, who in previous years had concluded that neutrinos traveled 730 kilometers faster than light.

Apparently, the conclusion previously given by CERN was due to a poor GPS connection at the time the experiment was performed (El tiempo, 2012).

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