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  • a

  • absolute constant
    An absolute constant is a number that has the same value wherever it appears. Examples:

    π (pi) has the value 3.14159…(...) - Read More

  • absolute space
    (Absolute space has recently been re-conceptualized and re-named as space that has "background-independence.")

    The(...) - Read More

  • absolute time
    The concept of absolute time was a foundational concept of physics as articulated by Isaac Newton in the 1600’s. It was(...) - Read More
  • acceleration
    Abbreviation: a

    In physics, acceleration is speeding up, slowing down, or changing direction. Acceleration contrasts(...) - Read More

  • action-at-a-distance

    Action-at-a-distance is the creation of an effect without physically touching. An example is magnetism: a magnet pulls(...) - Read More

  • algebraic constant
    An algebraic constant is a symbol that represents an unchanging number or is simply a number in an algebra equation. The(...) - Read More
  • alpha
    In quantum physics, the ancient Greek letter α, alpha, represents an important constant of nature. Alpha is .00729735256…(...) - Read More
  • amplitude of a wave
    The amplitude of a wave is its height, that is, half the distance from trough to crest.

    Carbon atoms on the surface of a crystal of graphite.(...) - Read More

  • atomic number
    The atomic number of an atom is the number of protons in its nucleus. For example, an atom of carbon has six protons and has(...) - Read More
  • b

  • B
    B is the symbol that represents the strength and direction, in any particular location, of the magnetic field due to the(...) - Read More
  • bare number
    For “bare number,” see “dimensionless number.” - Read More
  • baryon
    Baryons are a category of subatomic particles in the nucleus of the atom. Protons and neutrons are examples of baryons.(...) - Read More
  • baryonic matter
    All the matter that we ordinarily deal with in everyday life is baryonic matter. Baryonic matter is composed of atoms which(...) - Read More
  • Bohr atom
    Even though it’s now considered obsolete, Niels Bohr took a huge step forward in quantum physics, when in 1913, he proposed(...) - Read More
  • c

  • complex number
    This is an example of a complex number: 3 + 4i. It means take 3 and add 4 times i. The letter i is the symbol for the square(...) - Read More
  • conservation laws
    Physics includes several conservation laws. The most well-known is the Law of Conservation of Energy. This law states that(...) - Read More
  • conservation of energy
    The Law of Conservation of Energy says that in our universe the amount of energy remains constant. Energy cannot be created(...) - Read More
  • conservation of matter
    The Law of Conservation of Matter was abandoned as inaccurate by physicists early in the 1900’s. For more information, see(...) - Read More
  • conserved quantity
    A conserved quantity is something that remains constant in amount over time and cannot be created nor destroyed. Conserved(...) - Read More
  • constant

    A constant is a number or symbol that always has the same value. There are four types of constants:

    A mathematical(...) - Read More

  • constant of nature
    A constant of nature is another way of saying a "physical constant." - Read More
  • Coulomb's Law
    Coulomb’s Law is a formula that allows us to calculate the electric force generated between two electrical charges.(...) - Read More
  • d

  • dark energy
    Dark energy is the name given to an unexplained aspect of the universe. Dark energy has been postulated as an explanation(...) - Read More
  • dark matter
    "Dark matter" is a name that’s been given to a substance which many scientists believe may exist. If it exists, this(...) - Read More
  • dimensionless number
    Pi is an example of a dimensionless number. A dimensionless number doesn’t imply any measurement units. Pi is just 3.14, not(...) - Read More
  • e

  • e
    e is the symbol for Euler's number. Similarly to pi, e is a constant which occurs repeatedly throughout nature. It has a(...) - Read More
  • Euler's number (e)
    Euler's number, similarly to pi, is a constant which occurs repeatedly throughout nature. It is symbolized as e. It has a(...) - Read More
  • f

  • fine-structure constant
    See alpha, , α.  - Read More
  • frequency
    Frequency is the number of repeated motions in a period of time. These motions can be up and down, like a hammer, or back(...) - Read More
  • frequency and wavelength
    Frequency and wavelength are both properties of waves. They are closely related, so this article discusses the two(...) - Read More
  • function
    The term “function” is important in the field of quantum mechanics because is it the basis of the key term “wave function.”(...) - Read More
  • i

  • i
    The letter i is the symbol for the square root of -1. In other words i = √-1. The symbol i often appears in the equations of(...) - Read More
  • imaginary number
    An imaginary number is one that includes the square root of -1, written √(-1). While one might think that such a number(...) - Read More
  • ion
    An ion is formed when an atom gains or loses an electron. An atom which has lost one or more electrons has a positive(...) - Read More
  • ionize
    To ionize is to convert a substance from atomic or molecular form to ions.

    An ion is a type of atom that has an imbalance(...) - Read More

  • isotope
    Isotopes are a special kind of atom. Atoms with the same number of protons but different numbers of neutrons are isotopes of(...) - Read More
  • j

  • Joule
    A Joule is a unit for measuring energy. It's the amount of energy needed to lift a medium tomato one meter off the surface(...) - Read More
  • l

  • L
    (Symbol is L. Also called “rotational momentum” or “moment of momentum.”) Angular momentum is the momentum or oomph which an(...) - Read More
  • Law of Conservation of Energy
    The Law of Conservation of Energy says that the amount of energy in an isolated system remains constant. Energy cannot be(...) - Read More
  • Law of Conservation of Matter
    The Law of Conservation of Matter was abandoned as inaccurate by physicists early in the 1900’s. For more information, see(...) - Read More
  • linear momentum
    Linear momentum is the oomph something has due to having mass that’s in motion. If a football player were to ram into a(...) - Read More
  • lines of force
    “Lines of force” can best be explained with an illustration. The photo shows the lines of magnetic force created with a(...) - Read More
  • m

  • mathematical constant
    Pi and e are examples of mathematical constants. A mathematical constant has the same value no matter which mathematical(...) - Read More
  • metal
    A metal is a kind of matter, usually derived from rocks found in nature. Examples of metals include iron, aluminum, and(...) - Read More
  • moment
    “Moment,” as used in physics, means the amount of force experienced by an object due to the amount of force applied at a(...) - Read More
  • moment of force
    Moment of force is also called torque. “Moment,” as used in physics, means the amount of force experienced by an object due(...) - Read More
  • moment of momentum
    In classical physics, moment of momentum is the momentum or oomph which an object has as it rotates about an axis. It is the(...) - Read More
  • momentum
    (Abbreviated p. Momentum is the oomph something has due to having mass that’s in motion. Let’s say you just happen to be(...) - Read More
  • n

  • normal matter
    Scientists call the everyday matter of our world, such as tables and chairs, “normal matter.” Normal matter is made up of(...) - Read More
  • o

  • operator
    In mathematics, “operator” has two main definitions. 1) An operator is a mathematical symbol, for example +, that represents(...) - Read More
  • orbital angular momentum
    (Symbol: ɭ or L). Electrons have two types of rotational motion: orbital angular momentum and spin. Orbital angular momentum(...) - Read More
  • ordinary matter
    Scientists call the everyday matter of our world, such as tables and chairs, “ordinary matter.” Ordinary matter is made up(...) - Read More
  • oscillation
    Definition (1): An oscillation is a repetitive back-and-forth motion. A pendulum swinging back and forth is an everyday(...) - Read More
  • oscillator
    An oscillator is something that oscillates. Something that vibrates. See oscillation for more information.

    Billiard balls epitomize particles that follow Newton's Laws of(...) - Read More

  • period
    If you were standing on a dock and water waves were coming at you, the period would be the time interval between waves. In(...) - Read More
  • Periodic Table of the Elements
    The Periodic Table of the Elements lists all the elements, over 100 of them, in a specific sequence. This includes the(...) - Read More
  • physical constant
    The constant c, the speed of light in a vacuum, is an example of a physical constant. It is a constant of nature, always(...) - Read More
  • pi
    Pi is symbolized π and pronounced like "pie." It is the mathematical symbol for the number 3.14159…, which goes on(...) - Read More
  • probability amplitude
    “Probability amplitude” is a term used in quantum physics. It’s a number that appears in Schrodinger’s Wave Equation. Let’s(...) - Read More
  • q

  • QFT
    See Quantum Field Theory. - Read More
  • quantities of dimension one
    For “quantities of dimension one,” see “dimensionless number.” - Read More
  • quantum
    One definition of “quantum” is: a tiny packet of energy at the atomic level. A quantum is the smallest possible unit of(...) - Read More
  • quantum angular momentum
    For quantum angular momentum, see angular momentum. - Read More
  • Quantum Field Theory
    Quantum Field Theory (QFT) is the current theory of how atomic and subatomic particles behave. It is the most up-to-date(...) - Read More
  • quantum number
    Electrons have a few handfuls of properties. Four have been selected as the electron’s “quantum numbers.” The quantum(...) - Read More
  • quantum spin
    See "spin." - Read More
  • r

  • renormalization
    Renormalization is a technique for achieving greater precision in certain physics theories.* In quantum mechanics,(...) - Read More
  • rotational momentum
    Rotational momentum is the same thing as “angular momentum.” It is the momentum or oomph that an object has when it rotates(...) - Read More
  • s

  • scanning tunneling microscope
    A scanning tunneling microscope (STM) is a type of electron microscope. It is much more powerful than an ordinary microscope(...) - Read More
  • singularity
    “Singularity” has a physics definition and a mathematical definition. Both definitions are given here. They fit together(...) - Read More
  • Sommerfeld's Constant
    See alpha, α. - Read More
  • spin
    Spin is a property of subatomic and atomic particles. While spin was originally thought of as a particle twirling on its(...) - Read More
  • Stern-Gerlach device
    (Also called a “Stern-Gerlach machine.”) The Stern-Gerlach (SG) device detects the “quantum spin” of atoms and subatomic(...) - Read More
  • t

  • Tesla
    A Tesla is a unit for measuring the strength of magnetism in any particular location. A Tesla is approximately the strength(...) - Read More
  • torque
    For torque, see “moment of force.” - Read More
  • w

  • wave
    A wave is a movement that propagates through a medium. The accompanying animation demonstrates the motion of a seismic wave,(...) - Read More
  • wave equation
    This article starts with the nature of wave equations in classical physics and moves into a brief description of the(...) - Read More
  • waveform
    The waveform is the shape of a wave. Below is a graph on paper of a waveform representing the sound waves created by blowing(...) - Read More
  • wavelength
    Wavelength is a property of waves. It is the distance from wave crest to wave crest. Or from trough to trough—same distance.(...) - Read More
  • α

  • α
    In quantum physics, the ancient Greek letter α, alpha, represents an important constant of nature. Alpha is .00729735256…(...) - Read More
  • π

  • π
    See entry for pi. - Read More