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What Is Physics? Definition and Branches

Muhammad Rafiq is a freelance writer, blogger, and translator with a master's degree in English literature from the University of Malakand.


What Is Physics?

What is physics? This is a question with a long and complicated answer, but in short, it is the study of the natural world and the laws that govern it. Physics is concerned with everything from the smallest particles to the largest structures in the universe, and it is used to explain how everything works, from the basic principles of energy and matter to the complex behavior of subatomic particles and the cosmos as a whole.

In other words, physics is the science of understanding the universe and everything in it, from the smallest particles to the largest structures. It is used to explain how everything works, from the basic principles of energy and matter to the complex behavior of subatomic particles and the cosmos as a whole.

Definition of Physics

The following definitions of physics will further explain the question "What is Physics?":

According to the Oxford English Dictionary, physics is defined as:

Definition of Physics by the Oxford English Dictionary

"The branch of science concerned with the nature and properties of matter and energy. The subject matter of physics includes mechanics, heat, light and other radiation, sound, electricity, magnetism, and the structure of atoms."

Another definition by the digital encyclopedia Microsoft Encarta describes physics as:

Definition of Physics by Microsoft Encarta

“A major science dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces. Sometimes in modern physics a more sophisticated approach is taken that incorporates elements of the three areas listed above; it relates to the laws of symmetry and conservation, such as those pertaining to energy, momentum, charge, and parity.”

What these definitions indicate is that physics is a branch of science that deals with the properties of matter and energy and the relationship between them. It also tries to explain the material world and the natural phenomena of the universe.

The scope of physics is very wide and vast. It deals with not only the tiniest particles of atoms, but also natural phenomena like the galaxy, the milky way, solar and lunar eclipses, and more. While it is true that physics is a branch of science, there are many sub-branches within the field of physics. In this article, we will study various branches of physics in detail.

Importance of Physics

It is essential to our understanding of the universe, and its importance cannot be overstated. From the smallest particles to the largest structures in the cosmos, everything is governed by the laws of physics.

Through its investigations of the physical world, physics has led to the development of many important technologies that we take for granted today. From medical imaging to GPS, our world is full of applications that wouldn't be possible without a thorough understanding of physics.

In addition to its practical applications, physics is also a fascinating field of study in its own right. The quest to uncover the secrets of the universe has led to some of the most important scientific discoveries in history.

What Are the Branches of Physics?

While there are more branches sprouting up as science and technology progresses, there are generally 11 branches of physics. These are as follows.

11 Branches of Physics

  1. Classical physics
  2. Modern physics
  3. Nuclear physics
  4. Atomic physics
  5. Geophysics
  6. Biophysics
  7. Mechanics
  8. Acoustics
  9. Optics
  10. Thermodynamics
  11. Astrophysics

Continue reading to explore each of these branches in depth.

1. Classical Physics

Classical physics is one of the branches of physics that is mainly concerned with the laws of motion and gravitation as outlined in Sir Isaac Newton and James Clark Maxwell’s kinetic theory and thermodynamics, respectively. This branch of physics deals mostly with matter and energy. Often, physics which date before 1900 are considered classical physics, whereas physic which date after 1900 are considered modern physics.

In classical physics, energy and matter are considered separate entities. Acoustics, optics, classical mechanics, and electromagnetics are traditionally branches within classical physics. Moreover, any theory of physics that is considered null and void in modern physics automatically falls under the realm of classical physics.

As Newton's Laws are one of the main features of classical physics, let's examine them.

What Are the Three Laws of Physics?

The three laws of physics, as they are commonly referred to, are known formally as Newton's laws of motion. They are considered the basis of classical mechanics. Newton's laws describe the motion of a body upon which forces may act and which may exert forces on other bodies.

When we speak of bodies, we are not speaking of actual human bodies (although human bodies can be included in this definition), but of any piece of matter upon which a force may act. Newton's three laws are outlined below.

Newton's Laws of Motion (The Three Laws of Physics)

  1. Law of Inertia: A body remains at rest or in uniform motion in a straight line unless acted upon by a force.
  2. Force = Mass x Acceleration: A body's rate of change of momentum is proportional to the force causing it.
  3. Action = Reaction: When a force acts on a body due to another body, then an equal and opposite force acts simultaneously on that body.

2. Modern Physics

Modern physics is one of the branches of physics that is mainly concerned with the theory of relativity and quantum mechanics.

Albert Einstein and Max Plank were the pioneers of modern of physics as the first scientists to introduce the theory of relativity and quantum mechanics, respectively.

In modern physics, energy and matter are not considered as separate entities. Rather, they are considered different forms of each other.

What Are the Two Pillars of Modern Physics?

The two pillars of modern physics are as follows.

  1. Albert Einstein's theory of relativity
  2. Max Plank's quantum theory.

What Is the Theory of Relativity?

Albert Einstein's theory of relativity is one of the most important discoveries of the contemporary age, and states that the laws of physics are the same for all non-accelerating observers. As a result of this discovery, Einstein was able to confirm that space and time are interwoven in a single continuum known as space-time. As such, events that occur at the same time for one observer could occur at different times for another.

Einstein's theory of relativity is summarized in the formula:

E = mc^2

In this equation, "E" represents energy, "m" represents mass, and "c" represents the speed of light.

What Is Quantum Theory?

Discovered by Max Plank in 1900, quantum theory is the theoretical basis of modern physics that explains the nature and behaviour of matter and energy on the atomic and subatomic level. The nature and behaviour of matter and energy at that level is sometimes referred to as quantum physics and quantum mechanics.

Plank discovered that energy exists in individual units in the same way that matter does, rather than just as a constant electromagnetic wave. Thus, energy was quantifiable. The existence of these units, called quanta, act as the basis of Plank's quantum theory.

Nuclear physicists examine only the nucleus, not the atom as a whole.

Nuclear physicists examine only the nucleus, not the atom as a whole.

3. Nuclear Physics

Nuclear physics is one of the most fascinating and important branches of physics that deals with the constituents, structure, behaviour and interactions of atomic nuclei. This branch of physics should not be confused with atomic physics, which studies the atom as a whole, including its electrons.

According to the Microsoft Encarta encyclopedia, nuclear physics is defined as:

“The branch of physics in which the structure, forces, and behaviour of the atomic nucleus are studied.”

In the modern age, nuclear physics has become very wide in its scope and has been applied in many fields. It is used in power generation, nuclear weapons, medicines, magnetic resonance, imaging, industrial and agricultural isotopes, and more.

Who Discovered Nuclear Physics?

The history of nuclear physics as a distinct field from atomic physics begins with the discovery of radioactivity by Henri Becquerel in 1896. The discovery of the electron one year later indicated that the atom had an internal structure.

With this, studies began on the nuclei of atoms, thus nuclear physics was born.

4. Atomic Physics

Atomic physics is a branch of physics that deals with the composition of the atom apart from the nucleus. It is mainly concerned with the arrangement and behaviour of electrons in the shells around the nucleus. Thus, atomic physics mostly examines electrons, ions, and neutral atoms.

One of the earliest steps towards atomic physics was recognizing that all matter is comprised of atoms. The true beginning of atomic physics is marked by the discovery of spectral lines and the attempt to explain them. This resulted in an entirely new understanding of the structure of atoms and how they behave.

Computer simulation of the Earth's magnetic field in a period of normal polarity between reversals.

Computer simulation of the Earth's magnetic field in a period of normal polarity between reversals.

5. Geophysics

Geophysics is a branch of physics that deals with the study of the Earth. It is mainly concerned with the shape, structure and composition of the Earth, but geophysicists also study gravitational force, magnetic fields, earthquakes, magma, and more.

Geophysics was only recognized as a separate discipline in the 19th century, but its origins date back to ancient times. The first magnetic compasses were made from

All of these discoveries can be included in the field of geophysics, which is defined as:

"a natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis."

6. Biophysics

According to the Microsoft Encarta encyclopedia, biophysics is defined as:

“the interdisciplinary study of biological phenomena and problems, using the principles and techniques of physics.”

Biophysics studies biological problems and the structure of molecules in living organisms using techniques derived from physics. One of the most groundbreaking achievements of biophysics is the discovery of the structure of DNA (Deoxyribonucleic Acid) by James Watson and Francis Crick.

7. Mechanical Physics

Mechanical physics is one of the branches of physics that deals with the motion of material objects under the influence of forces.

Often called just mechanics, mechanical physics falls under two main branches:

  • Classical mechanics
  • Quantum mechanics

Classical mechanics deals with the laws of motion of physical objects and the forces that cause the motion, while quantum mechanics is the branch of physics which deals with the behaviour of smallest particles (i.e. electrons, neutrons, and protons).

What Are the Main Branches of Mechanics?

Mechanics can be broken down into eight sub-branches. These are as follows:

  1. Applied mechanics
  2. Celestial mechanics
  3. Continuum mechanics
  4. Dynamics
  5. Kinematics
  6. Kinetics
  7. Statics
  8. Statistical mechanics

8. Acoustics

The word "acoustics" is derived from a Greek word akouen, meaning "to hear."

Hence, we can define acoustics as a branch of physics that studies how sound is produced, transmitted, received and controlled. Acoustics also deals with the effects of sounds in various mediums (i.e. gas, liquid, and solids).

9. Optics

Optics is a branch of physics that studies electromagnetic radiation (for example, light and infrared radiation), its interactions with matter, and instruments used to gather information due to these interactions. Optics includes the study of sight.

The Microsoft Encarta encyclopedia defines optics as:

“a branch of physical science dealing with the propagation and behaviour of light. In a general sense, light is that part of the electromagnetic spectrum that extends from X rays to microwaves and includes the radiant energy that produces the sensation of vision.”

Who Invented Optics?

Optics began with the creation of lenses by the ancient Egyptians and Mesopotamians. This was followed up by theories of light and vision developed by ancient Greek philosophers and the development of geometric optics in the Greco-Roman world.

These earlier studies on optics are known as classical optics. Studies that came after the 20th century, such as wave optics and quantum optics, are known as modern optics.

10. Thermodynamics

Thermodynamics is one of those branches of physics that deals with heat and temperature and their relation to energy and work. The behaviour of these quantities is governed by the four laws of thermodynamics.

Who Discovered Thermodynamics?

The field of thermodynamics was developed from the work of Nicolas Léonard Sadi Carnot who believed that engine efficiency was the key that could help France win the Napoleonic Wars.

The Scottish physicist Lord Kelvin was the first to come up with a concise definition of thermodynamics. His definition stated:

"Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency."

What Are the Four Laws of Thermodynamics?

The four laws of thermodynamics are as follows.

  1. If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This law helps define the concept of temperature.
  2. When energy passes, as work, as heat, or with matter, into or out from a system, the system's internal energy changes in accord with the law of conservation of energy. Equivalently, perpetual motion machines of the first kind (machines that produce work with no energy input) are impossible.
  3. In a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases. Equivalently, perpetual motion machines of the second kind (machines that spontaneously convert thermal energy into mechanical work) are impossible.
  4. The entropy of a system approaches a constant value as the temperature approaches absolute zero. With the exception of non-crystalline solids (glasses), the entropy of a system at absolute zero is typically close to zero, and is equal to the natural logarithm of the product of the quantum ground states.

11. Astrophysics

The word "astrophysics" is a combination of two Latin-derived words: astro, which means "star," and phisis, which means "nature."

Thus, astrophysics can be defined as a branch of astronomy which is concerned with the study of universe (i.e., stars, galaxies, and planets) using the laws of physics.

What Is the Difference Between and Astrophysicist and an Astronomer?

Technically speaking, astronomers only measure the positions and characteristics of celestial bodies, whereas astrophysicists use the application physics to understand astronomy.

However, the terms are now used interchangeably, since all astronomers use physics to conduct their research.

By knowing these branches of physics, you can better understand the principles of physical phenomena, including how matter moves and interacts with energy and how it affects light and sound.


Is Physics Harder Than Math?

When it comes to the hard sciences, there is often a debate as to which discipline is more difficult: physics or math. Both disciplines require a great deal of mental fortitude and abstract thinking, so it is difficult to make a definitive statement about which one is harder. However, there are a few key differences between the two disciplines that may give physics the edge in terms of difficulty.

For one, physics often requires a more in-depth understanding of complex concepts. In math, there is often a definitive answer that can be arrived at through logical reasoning. In physics, however, the laws of the universe are often more elusive and can be open to interpretation. This means that students need to be able to think critically and analyze data in order to draw conclusions. Physics also often involves calculations with large numbers and complex equations, which can be daunting for students who are not strong in math. Hence, physics is generally considered to be more challenging than mathematics.

Is Physics Harder Than Biology?

It is difficult to make a direct comparison between physics and biology, as the two disciplines are quite different in nature. However, we can say that physics is generally considered to be more difficult than biology. This is because physics is a much more theoretical and abstract discipline than biology, which is more focused on empirical observation and experimentation. Physics also requires a strong understanding of mathematics, as many of its concepts are expressed in mathematical terms. Therefore, students who are struggling with mathematics may find physics to be particularly challenging.

Which Is More Difficult, Chemistry or Physics?

The debate of which science is more difficult, chemistry or physics, has been around for years. It is a difficult question to answer definitively because the two sciences are quite different in nature. However, we can examine the difficulty of each science in terms of the concepts that students must learn and the math skills required.

In terms of the concepts that students must learn, physics is generally considered to be more difficult than chemistry. Physics deals with abstract concepts such as energy, forces, and matter, while chemistry is mostly concerned with the properties and interactions of matter. These abstract concepts can be difficult for students to grasp, and they require a great deal of critical thinking to apply them to real-world situations.

However, physics is not only more difficult than chemistry in terms of the concepts that must be learned. Physics is also a more math-intensive subject than chemistry. Physics equations are often much more complex than those in chemistry, and students must be comfortable with using advanced math concepts in order to work through them. For many students, this can make physics seem like an insurmountable challenge.

What Is the Toughest Physics?

Quantum mechanics is often considered the hardest part of physics. This is because it deals with the behavior of particles on a very small scale, where the laws of classical physics no longer apply. Quantum mechanics can be very difficult to understand and apply, even for experienced physicists. Many physicists spend years studying quantum mechanics and still find it challenging to wrap their minds around it. If you're interested in pursuing a career in physics, be prepared to put in a lot of hard work to master quantum mechanics.

Why Is Physics So Hard?

Physics is often considered a difficult subject because it requires a deep understanding of mathematics and a strong grasp of scientific concepts. In addition, physics is constantly evolving, so students must be able to keep up with the latest discoveries. However, many people find physics fascinating and challenging, and the rewards of mastering the subject can be great. With perseverance and hard work, anyone can succeed in physics.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2015 Muhammad Rafiq


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