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Various examples of physical phenomena
Various examples of physical phenomena

Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves.

Physics is one of the oldest academic disciplines and, through its inclusion of astronomy, perhaps the oldest. Over much of the past two millennia, physics, chemistry, biology, and certain branches of mathematics were a part of natural philosophy, but during the Scientific Revolution in the 17th century these natural sciences emerged as unique research endeavors in their own right. Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other sciences and suggest new avenues of research in academic disciplines such as mathematics and philosophy.

Advances in physics often enable advances in new technologies. For example, advances in the understanding of electromagnetism, solid-state physics, and nuclear physics led directly to the development of new products that have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus. (Full article...)

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Hydrogen atomic orbitals at different energy levels. The more opaque areas are where one is most likely to find an electron at any given time.
Hydrogen atomic orbitals at different energy levels. The more opaque areas are where one is most likely to find an electron at any given time.

The electron is a subatomic particle (denoted by the symbol
) whose electric charge is negative one elementary charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy.

Electrons play an essential role in numerous physical phenomena, such as electricity, magnetism, chemistry and thermal conductivity, and they also participate in gravitational, electromagnetic and weak interactions. Since an electron has charge, it has a surrounding electric field, and if that electron is moving relative to an observer, said observer will observe it to generate a magnetic field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law. Electrons radiate or absorb energy in the form of photons when they are accelerated.

Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields. Special telescopes can detect electron plasma in outer space. Electrons are involved in many applications such as tribology or frictional charging, electrolysis, electrochemistry, battery technologies, electronics, welding, cathode ray tubes, photoelectricity, photovoltaic solar panels, electron microscopes, radiation therapy, lasers, gaseous ionization detectors and particle accelerators. (Full article...)
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  • ... that nuclear fusion reactions are probably occurring at or above the sun's photosphere; it is a process called solar surface fusion.
  • ... that a touch flash releases about a billion photons a second far less than produced in a particle accelerator?

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The current theoretical model of the atom involves a dense nucleus surrounded by a probabilistic "cloud" of electrons
The current theoretical model of the atom involves a dense nucleus surrounded by a probabilistic "cloud" of electrons

Atomic theory is the scientific theory that matter is composed of particles called atoms. Atomic theory traces its origins to an ancient philosophical tradition known as atomism. According to this idea, if one were to take a lump of matter and cut it into ever smaller pieces, one would eventually reach a point where the pieces could not be further cut into anything smaller. Ancient Greek philosophers called these hypothetical ultimate particles of matter atomos, a word which meant "uncut".

In the early 1800s, the scientist John Dalton noticed that chemical substances seemed to combine and break down into other substances by weight in proportions that suggested that each chemical element is ultimately made up of tiny indivisible particles of consistent weight. Shortly after 1850, certain physicists developed the kinetic theory of gases and of heat, which mathematically modelled the behavior of gases by assuming that they were made of particles. In the early 20th century, Albert Einstein and Jean Perrin proved that Brownian motion (the erratic motion of pollen grains in water) is caused by the action of water molecules; this third line of evidence silenced remaining doubts among scientists as to whether atoms and molecules were real. Throughout the nineteenth century, some scientists had cautioned that the evidence for atoms was indirect, and therefore atoms might not actually be real, but only seem to be real. (Full article...)
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Fundamentals: Concepts in physics | Constants | Physical quantities | Units of measure | Mass | Length | Time | Space | Energy | Matter | Force | Gravity | Electricity | Magnetism | Waves

Basic physics: Mechanics | Electromagnetism | Statistical mechanics | Thermodynamics | Quantum mechanics | Theory of relativity | Optics | Acoustics

Specific fields: Acoustics | Astrophysics | Atomic physics | Molecular physics | Optical physics | Computational physics | Condensed matter physics | Nuclear physics | Particle physics | Plasma physics

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Background: Physicists | History of physics | Philosophy of physics | Physics education | Physics journals | Physics organizations

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Physics topics

Classical physics traditionally includes the fields of mechanics, optics, electricity, magnetism, acoustics and thermodynamics. The term Modern physics is normally used for fields which rely heavily on quantum theory, including quantum mechanics, atomic physics, nuclear physics, particle physics and condensed matter physics. General and special relativity are usually considered to be part of modern physics as well.

Fundamental Concepts Classical Physics Modern Physics Cross Discipline Topics
Continuum Solid Mechanics Fluid Mechanics Geophysics
Motion Classical Mechanics Analytical mechanics Mathematical Physics
Kinetics Kinematics Kinematic chain Robotics
Matter Classical states Modern states Nanotechnology
Energy Chemical Physics Plasma Physics Materials Science
Cold Cryophysics Cryogenics Superconductivity
Heat Heat transfer Transport Phenomena Combustion
Entropy Thermodynamics Statistical mechanics Phase transitions
Particle Particulates Particle physics Particle accelerator
Antiparticle Antimatter Annihilation physics Gamma ray
Waves Oscillation Quantum oscillation Vibration
Gravity Gravitation Gravitational wave Celestial mechanics
Vacuum Pressure physics Vacuum state physics Quantum fluctuation
Random Statistics Stochastic process Brownian motion
Spacetime Special Relativity General Relativity Black holes
Quanta Quantum mechanics Quantum field theory Quantum computing
Radiation Radioactivity Radioactive decay Cosmic ray
Light Optics Quantum optics Photonics
Electrons Solid State Condensed Matter Symmetry breaking
Electricity Electrical circuit Electronics Integrated circuit
Electromagnetism Electrodynamics Quantum Electrodynamics Chemical Bonds
Strong interaction Nuclear Physics Quantum Chromodynamics Quark model
Weak interaction Atomic Physics Electroweak theory Radioactivity
Standard Model Fundamental interaction Grand Unified Theory Higgs boson
Information Information science Quantum information Holographic principle
Life Biophysics Quantum Biology Astrobiology
Conscience Neurophysics Quantum mind Quantum brain dynamics
Cosmos Astrophysics Cosmology Observable universe
Cosmogony Big Bang Mathematical universe Multiverse
Chaos Chaos theory Quantum chaos Perturbation theory
Complexity Dynamical system Complex system Emergence
Quantization Canonical quantization Loop quantum gravity Spin foam
Unification Quantum gravity String theory Theory of Everything

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