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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.")

• 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.

In classical physics, angular momentum is the momentum or oomph which an object has as it rotates about an axis or follows a circular path, for example, a planet’s orbit around the sun. Angular momentum is measured by the force required to stop a rotating object. In quantum physics, angular momentum is of two types: 1) inherent angular momentum (spin) and 2) orbital angular momentum. Angular momentum in quantum physics has been named as such on analogy with angular momentum in classical physics. However, there are major dissimilarities between the two.

">angular momentum

(Symbol is L. Also called “rotational momentum” or “moment of momentum.”) Angular momentum is the momentum or oomph which an(...) - Read More
• anomaly
An anomaly is an experimental result or an observation that doesn’t fit current scientific theories.

• antimatter
Antimatter is not just the stuff of science fiction. It is as real as ordinary matter. Physicists call the matter that we(...) - Read More
• antiparticle
An antiparticle is an antimatter version of a normal particle. For example, an antiquark is an antimatter quark. An(...) - Read More
• atom

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
• 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:

• 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.

Momentum is the oomph something has due to having mass that’s in motion. If a football player were to ram into a bystander at full speed, he would hit the bystander with great momentum (large mass at high speed). Momentum is also called “linear momentum.” It is symbolized: p. Angular momentum is different.

">p

(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
• particle
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
• 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
• ## 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