Category: Dictionary

hertz : The SI unit of frequency, defined as the number of cycles per second of a periodic phenomenon.

heat: A form of energy transferred from one body to another by thermal interaction.

half-life : The time required for a quantity to fall to half its value as measured at the beginning of the time period. In physics, half-life typically refers to a property of radioactive decay, but may refer to any quantity which follows an exponential decay.

gravity : See gravitation.

gravitational wave : A ripple in the curvature of spacetime that propagates as a wave and is generated in certain gravitational interactions, travelling outward from their source.

gravitational potential : The gravitational potential at a location is equal to the work (energy transferred) per unit mass that is done by the force of gravity to move an object to a fixed reference location.

gravitational field : A model used to explain the influence that a massive body extends into the space around itself, producing a force (gravity) on another massive body. Thus, a gravitational field is used to explain and represent gravitational phenomena. It is measured in newtons per kilogram (N/kg).

gravitational energy : The potential energy associated with the gravitational field.

gravitational constant (G): Also called the universal gravitational constant and Newton’s constant.

A physical constant involved in the calculation of gravitational force between two bodies.

gravitation: Also called gravity.

A natural phenomenon by which physical bodies attract each other with a force proportional to their masses.

gamma ray : A form of electromagnetic radiation of very high frequency and therefore very high energy.

fusion : A nuclear reaction in which two or more atomic nuclei join together, or “fuse”, to form a single heavier nucleus.

fundamental forces: Also called fundamental interactions.

freezing point : The temperature at which a substance changes state from liquid to solid.

lever : A type of machine consisting of a beam or rigid rod pivoted at a fixed hinge or fulcrum; one of six classical simple machines.

force (F) : Any interaction that, when unopposed, will change the motion of a physical body. A force has both magnitude and direction, making it a vector quantity. The SI unit used to measure force is the newton.

fission : Either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons (in the form of gamma rays) and releasing relatively large amounts of energy.

entropy : A quantity which describes the randomness of a substance or system.

fermion : A type of particle that behaves according to Fermi–Dirac statistics, obeys the Pauli exclusion principle, and possesses half-integer spin. Fermions include all quarks and leptons, as well as all composite particles made of an odd number of these (such as all baryons and many atoms and nuclei). Fermions constitute one of two main classes of particles, the other being bosons.

falling bodies : Objects that are moving towards a body with greater gravitational influence, such as a planet.

exothermic : An adjective used to refer to a process or reaction that releases energy from a system, usually in the form of heat but also in the form of light, electricity, or sound. Contrast endothermic.

escape velocity : The velocity at which the kinetic energy plus the gravitational potential energy of an object is zero. It is the speed needed to “escape” from a gravitational field without further propulsion.

endothermic : An adjective used to refer to a process or reaction in which a system absorbs energy from its surroundings, usually in the form of heat but also in the form of light, electricity, or sound. Contrast exothermic.

energy : The ability to do work.

electronics : A field that deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes, and integrated circuits as well as associated passive interconnection technologies.

electronegativity : A chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself.

electronvolt (eV) : A unit of energy equal to approximately 1.6×10⁻¹⁹ joule. By definition, it is the amount of energy gained by the charge of a single electron moved across an electric potential difference of one volt.

electron paramagnetic resonance:Also called electron spin resonance (ESR) and electron magnetic resonance (EMR).

A method for studying materials with unpaired electrons which makes use of the Zeeman effect. It shares some basic principles with nuclear magnetic resonance (NMR).

electron : A subatomic particle with a negative elementary electric charge.

electromotive force: Also abbreviated emf.

The electrical intensity or “pressure” developed by a source of electrical energy such as a battery or generator and measured in volts. Any device that converts other forms of energy into electrical energy provides electromotive force as its output.

electromagnetic radiation: Also abbreviated EM radiation or EMR.

A form of energy emitted and absorbed by charged particles, which exhibits wave-like behavior as it travels through space.

electromagnetic field: Also abbreviated EM field or EMF.

A physical field produced by moving electrically charged objects.

electromagnet : A type of magnet in which the magnetic field is produced by the flow of electric current.

electricity: The set of physical phenomena associated with the presence and flow of electric charges.

electrical resistance : The opposition to the passage of an electric current through an electrical element.

electrical network : An interconnection of electrical elements such as resistors, inductors, capacitors, voltage sources, current sources, and switches.

electrical insulator : Any material whose internal electric charges do not flow freely and which therefore does not conduct an electric current under the influence of an electric field.

electrical conductor : Any material which contains movable electric charges and therefore can conduct an electric current under the influence of an electric field.

electric power: The rate at which electric energy is transferred by an electric circuit.

electric field: The region of space surrounding electrically charged particles and time-varying magnetic fields. The electric field represents the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding.

electric current : A flow of electric charge through a conductive medium.

electric circuit : An electrical network consisting of a closed loop, giving a return path for the current.