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Overview by Joan Omoruyi, Subject Librarian at Northeastern University

What Is Physics?

Physics can be described as the scientific study of matter and energy and how they interact with each other over space and time. Since the concepts in physics are basic to all phenomena, it has been said that physics is the foundation of all science. Physics has been called the "king of sciences."

Physics deals with matter on scales ranging from sub-atomic particles (i.e. the particles that make up the atom and the particles that make up those particles) to stars and even entire galaxies. Energy can take many forms including motion, light, electricity, radiation or gravity.

Physics explores the laws of the universe and follows the journey of those who tried to understand the world around them. A few well known physicists include Albert Einstein, Richard P. Feynman, Niels Bohr and Sir Isaac Newton.

Physicists must be comfortable with mathematics and must be able to apply mathematical concepts. In addition, knowledge of the scientific method* is essential, as well as knowledge of the other tools used by physicists. Do you know that it was physicists who created the world wide web so they could easily communicate and share information among themselves?

*The scientific method is a process for experimentation that is used to explore observations and answer questions. Scientists use the scientific method to search for cause and effect relationships in nature. In other words, they design an experiment so that changes to one item cause something else to vary in a predictable way.

Aim of Physics

The aim of physics is to understand how nature works. One of the ideas of physics is that behind the apparently complex world is an underlying simplicity and unity. In the attempt to understand the physical world, careful observation and experimentation are made and the results analyzed, and as a result theories develop. Predictions made from theories can lead to the theory being refined or to a conflict which may be serious enough to reject the theory.

Why is Physics Important?

  • Physics is integral to society.
  • It generates the knowledge for technology.
  • It expands our horizons and pushes back the frontiers of knowledge.
  • It plays a vital role in the education of many types of scientists: engineers, chemists, meteorologists, astronomers and many of the medical sciences.
  • Physics has provided us with many comforts, e.g. electricity and the telephone.
  • Physics helps extend lives by its contributions to medicine.

Branches of Physics

Physics can be divided into many branches that deal with the broad classes of natural phenomena. These branches include:

  • Mechanics. This is one of the oldest branches and was developed by Isaac Newton in the seventeenth century. Mechanics deals with motion, force, energy and inertia, and how these act on solids and fluids.
  • Thermodynamics and heat. The study of heat involves the principles of temperature measurement, heat flow and the effect of heat on the properties of matter. Thermodynamics is related to heat and is the study of the effects of the change of pressure, density, volume and temperature, etc. on physical systems.
  • Elecromagnetism. In the nineteenth century James Clerk Maxwell discovered that electricity and magnetism were actually manifestations of the same underlying phenomena, which came to be called electromagnetism. An example is that a moving particle with an electric charge produces or induces a magnetic field.

The study of light led to the field of optics which is the study of the nature and propagation of light and its refraction through various transparent media. Light can be separated into various frequencies which are known as spectra. It is the understanding of spectra that provides information about the elements, the stars and other celestial bodies.

Modern Physics

There is an area of physics called modern physics which includes atomic physics, quantum mechanics, relativity theory, nuclear physics and solid state physics.

Atomic physics is the study of atoms, specifically the electron properties of the atom.

Quantum mechanics developed in the late 1920’s and is fundamental to all physics. The word quantum in physics refers to the smallest discrete quantity of a physical property. Quantum mechanics explains how electrons move around the nucleus of the atom and what happens when they jump between orbitals as they move around. Quantum theory is based on the idea of a quantum, the idea that energy is assumed to come in small units. The smallest values or quanta of matter and energy become relevant. The application of quantum theory has resulted in many modern marvels, such as computers, digital watches, television and lasers.

Relativity shows that mass and energy are proportional (E-mc2). It is the study of systems displaying the properties of Einstein’s theory of relativity, the theory that space and time are relative concepts rather than absolute concepts (E=mc2). This theory usually involves objects moving at speeds very close to the speed of light, which moves at 186,000 miles a second or 700 million miles an hour. It also

  • explains the source of energy for the sun and stars;
  • gave new insight into gravity. Newton described gravity as force at a distance, however according to relativity gravity is curved space;
  • has made it possible for scientists to understand neutron stars and black holes, and by doing that has given profound insight into the workings of the universe.

The phenomenon of waves has an important role throughout physics. Sound is a wave. In the nineteenth century it was found that electricity and magnetism together create electromagnetic waves. Examples of electromagnetic waves are light, ultraviolet, infrared and X-rays and radio waves.

Fundamental Forces. In physics there is an important concept of forces. The four fundamental forces of physics are gravity, electromagnetism, weak interaction, and strong interaction. These fundamental forces (or fundamental interactions) are the ways that individual particles interact with each other. It turns out that every single interaction that has been observed to take place in the universe, can be described by only these four types of interactions.

Gravity is the weakest but has the greatest reach. It is gravity that reaches through space to draw masses toward each other. Gravity keeps the planets in orbit around the sun and the moon in orbit around the earth. It is a purely attractive force which reaches through even the "empty" void of space to draw two masses toward each other. It keeps the planets in orbit around the sun and the moon in orbit around the Earth.

Einstein’s theory of general relativity defines gravity as the curvature of space-time around an object of mass. The curvature creates a situation where the path of least energy is toward the other object of mass.

Gravitation is described under the theory of general relativity, which defines it as the curvature of spacetime around an object of mass. This curvature, in turn, creates a situation where the path of least energy is toward the other object of mass.

Electromagnetism is the interaction of particles with an electric charge. Charged particles, at rest interact through electrostatic forces, while in motion they interact with both electrical and magnetic forces.

Electric and magnetic forces used to be as considered to be different forces. However in 1864. James Clerk Maxwell unified them under Maxwell’s equations. In the 1940’s quantum electrodynamics consolidated electromagnetism and quantum physics.

Electromagnetism can affect things at a reasonable distance and with a fair amount of force.

Weak Interaction is not a weak but a very powerful force that acts on the scale of the atomic nucleus. It causes such phenomena as beta decay. The weak interaction is a very powerful force that acts on the scale of the atomic nucleus. It causes phenomena such as beta decay. It has been consolidated with electromagnetism as a single interaction called the "electroweak interaction."

Strong Interaction. This is the strongest of the forces. It keeps nudeons (protons) and (neutrons) bound together.

In the helium atom, for example, it is strong enough to bind two protons together despite the fact that their positive electrical charges cause them to repulse each other.

The strong interaction allows particles called gluons to bind together quarks to create the nucleons in the first place. Gluons can also interact with other gluons, which gives the strong interaction a theoretically infinite distance, although it's major manifestations are all at the subatomic level.

Unifying the Fundamental Forces

Many physicists believe that all four of the fundamental forces are, in fact, the manifestations of a single underlying (or unified) force which has yet to be discovered.

The current quantum mechanical interpretation of these forces is that the particles do not interact directly, but rather manifest virtual particles that mediate the actual interactions. All of the forces except for gravity have been consolidated into this "Standard Model" of interaction.

The effort to unify gravity with the other three fundamental forces is called quantum gravity. It postulates the existence of a virtual particle called the graviton, which would be the mediating element in gravity interactions.

Subfields of Physics

Basic physics has been applied to other disciplines and has resulted in a number of subfields. These subfields include:

  • Astrophysics – this is a branch of astronomy which deals with the behavior, physical properties and dynamic processes of celestial objects and phenomena.
  • Atmospheric physics - the application of mathematics and physical models to the understanding of the atmosphere of earth and other planets.
  • Biophysics – applies physical principles and methods to biological problems.
  • Cryophysics or low temperature physics.
  • Geophysics or physics of the earth.
  • Molecular physics – the study of physical properties of molecules.
  • Nuclear physics – the study of the physical properties of the atomic nucleus.
  • Nanotechnology – the science of building circuits and machines from single molecules and atoms.
  • Particle physics* - is the study of fundamental particles and the forces of their interaction.
  • Physical oceanography - the study of the physical structure, movement, and properties of the oceans.

* The Scientific world is very interested in the Large Hadron Collider (LHC), a particle-physics laboratory near Geneva. Hadron is a name for sub-atomic particles such as neutrons and protons. This particle accelerator was built by the European Organization for Nuclear Research (CERN) to be used by physicists to study the smallest known particles – the fundamental building blocks of all things. This collider will try to replicate conditions that existed after the Big Bang and is expected to revolutionize the understanding scientists have of the world deep within atoms to the vastness of the universe.


NASA. Goddard Space Flight Center. Imagine the Universe Dictionary. [Internet] Available from: [November, 2010]

New physics for the twenty-first century. Fraser, Gordon, ed. Cambridge, NY. 2003.

Parker, Brian, Smithsonian Institution. Physics. New York, NY. Collins, 2007.

Physics Resources

  • ComPADRE "The AAPT ComPADRE Digital Library s a network of free online resource collections supporting faculty, students, and teachers in Physics and Astronomy Education."
  • Hyperphysics – Online tutorials cover a wide range of physics topics, including modern physics and astronomy. Material is organized through extensive concept maps.
  • The Particle Adventure:  The Fundamentals of Matter and Force-an interactive tour of quarks, neutrinos, antimatter, extra dimensions, dark matter, accelerators, and particle detectors from the Particle Data Group.
  • PhET Physics Education Technology has simulations in physics, math, and other sciences.
  • Science Tracer Bullets Online The Science Tracer Bullet Series from the Library of Congress "contains research guides that help you locate information on science and technology subjects."