Physics | Definition, Types, Topics, Importance, & Facts (2024)

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Written by

Richard Tilghman Weidner Emeritus Professor of Physics, Rutgers University, New Brunswick, New Jersey. Author of Physics and others.

Richard Tilghman Weidner,

Laurie M. Brown Emeritus Professor of Physics and Astronomy, Northwestern University, Evanston, Illinois. Coeditor of The Birth of Particle Physics.

Laurie M. BrownAll

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Bernoulli model of gas pressure

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Key People:
Edward Alexander Bouchet
Fabiola Gianotti
Charles H. Bennett
Anne L’Huillier
Kip Thorne
Related Topics:
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optics
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cosmology
gravity

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Top Questions

What is physics?

Physics is the branch of science that deals with the structure of matter and how the fundamental constituents of the universe interact. It studies objects ranging from the very small using quantum mechanics to the entire universe using general relativity.

Why does physics work in SI units?

Physicists and other scientists use the International System of Units (SI) in their work because they wish to use a system that is agreed upon by scientists worldwide. Since 2019 the SI units have been defined in terms of fundamental physical constants, which means that scientists anywhere using SI can agree upon the units they use to measure physical phenomena.

physics, science that deals with the structure of matter and the interactions between the fundamental constituents of the observable universe. In the broadest sense, physics (from the Greek physikos) is concerned with all aspects of nature on both the macroscopic and submicroscopic levels. Its scope of study encompasses not only the behaviour of objects under the action of given forces but also the nature and origin of gravitational, electromagnetic, and nuclear force fields. Its ultimate objective is the formulation of a few comprehensive principles that bring together and explain all such disparate phenomena.

(Read Einstein’s 1926 Britannica essay on space-time.)

Physics is the basic physical science. Until rather recent times physics and natural philosophy were used interchangeably for the science whose aim is the discovery and formulation of the fundamental laws of nature. As the modern sciences developed and became increasingly specialized, physics came to denote that part of physical science not included in astronomy, chemistry, geology, and engineering. Physics plays an important role in all the natural sciences, however, and all such fields have branches in which physical laws and measurements receive special emphasis, bearing such names as astrophysics, geophysics, biophysics, and even psychophysics. Physics can, at base, be defined as the science of matter, motion, and energy. Its laws are typically expressed with economy and precision in the language of mathematics.

Both experiment, the observation of phenomena under conditions that are controlled as precisely as possible, and theory, the formulation of a unified conceptual framework, play essential and complementary roles in the advancement of physics. Physical experiments result in measurements, which are compared with the outcome predicted by theory. A theory that reliably predicts the results of experiments to which it is applicable is said to embody a law of physics. However, a law is always subject to modification, replacement, or restriction to a more limited domain, if a later experiment makes it necessary.

Britannica QuizAnother Physics Quiz

The ultimate aim of physics is to find a unified set of laws governing matter, motion, and energy at small (microscopic) subatomic distances, at the human (macroscopic) scale of everyday life, and out to the largest distances (e.g., those on the extragalactic scale). This ambitious goal has been realized to a notable extent. Although a completely unified theory of physical phenomena has not yet been achieved (and possibly never will be), a remarkably small set of fundamental physical laws appears able to account for all known phenomena. The body of physics developed up to about the turn of the 20th century, known as classical physics, can largely account for the motions of macroscopic objects that move slowly with respect to the speed of light and for such phenomena as heat, sound, electricity, magnetism, and light. The modern developments of relativity and quantum mechanics modify these laws insofar as they apply to higher speeds, very massive objects, and to the tiny elementary constituents of matter, such as electrons, protons, and neutrons.

The scope of physics

The traditionally organized branches or fields of classical and modern physics are delineated below.

Mechanics

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Mechanics is generally taken to mean the study of the motion of objects (or their lack of motion) under the action of given forces. Classical mechanics is sometimes considered a branch of applied mathematics. It consists of kinematics, the description of motion, and dynamics, the study of the action of forces in producing either motion or static equilibrium (the latter constituting the science of statics). The 20th-century subjects of quantum mechanics, crucial to treating the structure of matter, subatomic particles, superfluidity, superconductivity, neutron stars, and other major phenomena, and relativistic mechanics, important when speeds approach that of light, are forms of mechanics that will be discussed later in this section.

In classical mechanics the laws are initially formulated for point particles in which the dimensions, shapes, and other intrinsic properties of bodies are ignored. Thus in the first approximation even objects as large as Earth and the Sun are treated as pointlike—e.g., in calculating planetary orbital motion. In rigid-body dynamics, the extension of bodies and their mass distributions are considered as well, but they are imagined to be incapable of deformation. The mechanics of deformable solids is elasticity; hydrostatics and hydrodynamics treat, respectively, fluids at rest and in motion.

The three laws of motion set forth by Isaac Newton form the foundation of classical mechanics, together with the recognition that forces are directed quantities (vectors) and combine accordingly. The first law, also called the law of inertia, states that, unless acted upon by an external force, an object at rest remains at rest, or if in motion, it continues to move in a straight line with constant speed. Uniform motion therefore does not require a cause. Accordingly, mechanics concentrates not on motion as such but on the change in the state of motion of an object that results from the net force acting upon it. Newton’s second law equates the net force on an object to the rate of change of its momentum, the latter being the product of the mass of a body and its velocity. Newton’s third law, that of action and reaction, states that when two particles interact, the forces each exerts on the other are equal in magnitude and opposite in direction. Taken together, these mechanical laws in principle permit the determination of the future motions of a set of particles, providing their state of motion is known at some instant, as well as the forces that act between them and upon them from the outside. From this deterministic character of the laws of classical mechanics, profound (and probably incorrect) philosophical conclusions have been drawn in the past and even applied to human history.

Lying at the most basic level of physics, the laws of mechanics are characterized by certain symmetry properties, as exemplified in the aforementioned symmetry between action and reaction forces. Other symmetries, such as the invariance (i.e., unchanging form) of the laws under reflections and rotations carried out in space, reversal of time, or transformation to a different part of space or to a different epoch of time, are present both in classical mechanics and in relativistic mechanics, and with certain restrictions, also in quantum mechanics. The symmetry properties of the theory can be shown to have as mathematical consequences basic principles known as conservation laws, which assert the constancy in time of the values of certain physical quantities under prescribed conditions. The conserved quantities are the most important ones in physics; included among them are mass and energy (in relativity theory, mass and energy are equivalent and are conserved together), momentum, angular momentum, and electric charge.

Physics | Definition, Types, Topics, Importance, & Facts (2024)

FAQs

What is the most important topic in physics? ›

JEE Main Important Chapters & Topics for Physics
High WeightageLow Weightage
Heat & ThermodynamicsHeat Transfer
Ray OpticsFluids
Electromagnetic WavesNuclear Physics & X-Rays
SemiconductorsWork, Energy & Power
14 more rows

What is the topic of importance of physics? ›

Physics is playing a vital role in everyday life and is involved in a number of activities we perform in our daily life for example walking, cooking cutting, vision and may more activities. All these activities are involve the principles of physics. Asking importance of physics is like importance of nature itself.

What are 4 topics commonly studied in physics? ›

Some of the topics in physics that are common in most fields include thermodynamics, Newton's laws, relativity theory, quantum mechanics, optics, and electricity and magnetism.

What are the 12 branches of physics? ›

  • Classical mechanics.
  • Thermodynamics and statistical mechanics.
  • Electromagnetism and photonics.
  • Relativistic mechanics.
  • Quantum mechanics, atomic physics, and molecular physics.
  • Optics and acoustics.
  • Condensed matter physics.
  • High-energy particle physics and nuclear physics.

What is the most confusing physics topic? ›

  1. Quantum Gravity. The biggest unsolved problem in fundamental physics is how gravity and the quantum will be made to coexist within the same theory. ...
  2. Particle Masses. ...
  3. The “Measurement” Problem. ...
  4. Turbulence. ...
  5. Dark Energy. ...
  6. Dark Matter. ...
  7. Complexity. ...
  8. The Matter-Antimatter.

What are the 6 main areas of physics and its importance? ›

Physics is organised into a large number of branches, each of which focuses on a different aspect of the subject. Atomic and nuclear Physics , acoustics, optics, astronomy, geoPhysics , thermodynamics, and many more fields of Physics are among the most well-known.

What is the most important thing to learn in physics? ›

At the heart of physics is a combination of experiment, observation and the analysis of phenomena using mathematical and computational tools. Examples of what physicists study include: The nature of fundamental particles (protons, quarks, electrons, neutrinos,…).

What are the most important basic in physics? ›

The conserved quantities are the most important ones in physics; included among them are mass and energy (in relativity theory, mass and energy are equivalent and are conserved together), momentum, angular momentum, and electric charge.

What are the 7 major areas of physics? ›

The seven branches of physics are optics, electromagnetism, relativity, thermodynamics, acoustics, quantum physics, and mechanics. There are smaller categories within these broad areas.

What are the 4 pillars of physics? ›

There are actually four pillars:
  • Special Relativity (Electrodynamics)
  • General Relativity (Gravity)
  • Quantum Mechanics (Matter and Energy)
  • The Big Bang (Cosmology)
Jul 31, 2019

What is the hardest branch of physics? ›

What Is the Most Difficult Branch of Physics?
  • General Relativity. ...
  • Statistical Mechanics. ...
  • Plasma Physics. ...
  • Condensed Matter Physics. ...
  • Quantum Field Theory. ...
  • Nuclear Physics. ...
  • Non-linear Dynamics and Chaos Theory. ...
  • Electrodynamics. The physics of electric charges in motion.

What is the oldest branch of physics? ›

Classical Physics is the oldest branch of Physics.

What are the 3 fields in physics? ›

The three types of fields in physics are: scalar, vector, and tensor fields. Scalar fields describe things that only have a magnitude. Vector fields describe things that have two pieces of information (magnitude and direction). Tensor fields describe things that have three pieces of information.

What is the most important thing in physics? ›

The conserved quantities are the most important ones in physics; included among them are mass and energy (in relativity theory, mass and energy are equivalent and are conserved together), momentum, angular momentum, and electric charge.

Which part of physics is important? ›

These central theories are important tools for research into more specialized topics, and any physicist, regardless of their specialization, is expected to be literate in them. These include classical mechanics, quantum mechanics, thermodynamics and statistical mechanics, electromagnetism, and special relativity.

What is the most important rule of physics? ›

1. Newton's Laws of Motion: Sir Isaac Newton's laws of motion laid the foundation for classical mechanics and our understanding of motion: Newton's First Law (Law of Inertia): An object at rest remains at rest, and an object in motion continues to move at a constant velocity unless acted upon by an external force.

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