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weak force

or weak nuclear force

Fundamental interaction that underlies some forms of radioactivity and certain interactions between subatomic particles. It acts on all elementary particles that have a spin of 12. The particles interact weakly by exchanging particles that have integer spins. These particles have masses about 100 times that of a proton, and it is this relative massiveness that makes the weak force appear weak at low energies. For example, in radioactive decay, the weak force has a strength about 1/100,000 that of the electromagnetic force. However, it is now known that the weak force has intrinsically the same strength as the electromagnetic force, and the two are believed to be only different manifestations of a single electroweak force (see electroweak theory).

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or strong nuclear force

Fundamental force acting between elementary particles of matter, mainly quarks. The strong force binds quarks together in clusters to form protons and neutrons and heavier short-lived particles. It holds together the atomic nucleus and underlies interactions among all particles containing quarks. In strong interactions, quarks exchange gluons, carriers of the strong force, which are massless particles with one unit of intrinsic spin. Within its short range (about 10−15 m), the strong force appears to become stronger with distance. At such distances, the strong interaction between quarks is about 100 times greater than the electromagnetic force.

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Universal force of attraction that acts between all bodies that have mass. Though it is the weakest of the four known forces, it shapes the structure and evolution of stars, galaxies, and the entire universe. The laws of gravity describe the trajectories of bodies in the solar system and the motion of objects on Earth, where all bodies experience a downward gravitational force exerted by Earth's mass, the force experienced as weight. Isaac Newton was the first to develop a quantitative theory of gravitation, holding that the force of attraction between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. Albert Einstein proposed a whole new concept of gravitation, involving the four-dimensional continuum of space-time which is curved by the presence of matter. In his general theory of relativity, he showed that a body undergoing uniform acceleration is indistinguishable from one that is stationary in a gravitational field.

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Statement that any particle of matter in the universe attracts any other with a force (math.F) that is proportional to the product of their masses (math.m1 and math.m2) and inversely proportional to the square of the distance (math.R) between them. In symbols: math.F = math.G(math.m1math.m2)/math.R2, where math.G is the gravitational constant. Isaac Newton put forth the law in 1687 and used it to explain the observed motions of the planets and their moons, which had been reduced to mathematical form by Johannes Kepler early in the 17th century.

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In physics, the effect of any of the four fundamental forces—gravitational, electromagnetic, strong, and weak. All known natural forces can be traced to these fundamental interactions. Gravitation is the attractive force between any two objects that have mass; it causes objects to fall to the ground and maintains the orbits of planets around the Sun. Electromagnetic force is responsible for the attraction and repulsion between electric charges and explains the chemical behaviour of atoms and the properties of light. The strong force binds quarks together in protons, neutrons, and other hadrons and also holds the protons and neutrons of an atomic nucleus together, overcoming the repulsion of the positively charged protons for each other. The weak force is observed in certain forms of radioactive decay (see radioactivity) and in reactions that fuel the Sun and other stars.

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One of the four known basic forces in the universe. Electromagnetism is responsible for interactions between charged particles that occur because of their charge, and for the emission and absorption of photons (electromagnetic radiation). The phenomena of electricity and magnetism are consequences of this force, and the relationships between them were first described by James Clerk Maxwell in the 1860s. The physical description of electromagnetism has since been combined with quantum mechanics into the theory of quantum electrodynamics. The electromagnetic force is about 1036 times as strong as the gravitational force (see gravitation), but significantly weaker than both the weak force and the strong force.

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Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way causal effect. A closely related term is interconnectivity, which deals with the interactions of interactions within systems: combinations of many simple interactions can lead to surprising emergent phenomena. Interaction has different tailored meanings in various sciences. All systems are related and interdependent. Every action has a consequence.

Casual examples of interaction outside of science include:

Chemistry and medicine

In medicine, most medications can be safely used with other medicines, but particular combinations of medicines need to be monitored for interactions, often by the pharmacist. In molecular biology, the knowledge on gene/protein interaction among themselves and with their metabolites is referred to as molecular pathways.

Interactions between medications (drug interactions) fall generally into one of two main categories:

  1. pharmacodynamic : Involving the actions of the two interacting drugs.
  2. pharmacokinetic : Involving the absorption, distribution, metabolism, and excretion of one or both of the interacting drugs upon the other.

In terms of efficacy, there can be three types of interactions between medications: additive, synergistic, and antagonistic. Additive interaction means the effect of two chemicals is equal to the sum of the effect of the two chemicals taken separately. This is usually due to the two chemicals acting on the body in the same way. Examples would be Aspirin and Motrin, Alcohol and Depressant, Tranquilizer and Painkiller. Synergistic interaction means that the effect of two chemicals taken together is greater than the sum of their separate effect at the same doses. An example is Pesticide and Fertilizer, the biological effect is devastating. Antagonistic interaction means that the effect of two chemicals is actually less than the sum of the effect of the two drugs taken independently of each other. This is because the second chemical increases the excretion of the first, or even directly blocks its toxic actions. Antagonism forms the basis for antidotes of poisonings. An example is Asparagus and birth control pills.


In communications, interactive communication occurs when sources take turns transmitting messages between one another. This should be distinguished from transactive communication, in which sources transmit messages simultaneously. Included in this category are all new modes of communication such as cable video, teletext, videotext, teleshopping, video on demand, computers, Internet, tele-conferencing etc. Tele-communication also falls under this category. so cell phones, pagers, mobile phones, and electronic mail are interactive communications. these can be classified under three headings:

  1. Interpersonal : Telephone and its allied services.
  2. Group : Tele-conference. video-conference.
  3. Mass : Internet, world wide web

Media art

In media, interactivity is a feature of the media in question and as digital technology becomes more accessible to the masses interest in interactivity is increasing and becoming a cultural trend especially in the arts.


In physics, an interaction or force specifically refers to the action of one physical object upon another and results in a potential energy - the physical objects under consideration may range from point particles to quantum fields. For example, the interaction of charged particles takes place through the mediation of electromagnetic fields, whereas beta decay occurs by means of the weak interaction. There are believed to be four fundamental interactions in Nature.


In sociology, social interaction is a dynamic, changing sequence of social actions between individuals (or groups) who modify their actions and reactions due to the actions by their interaction partner(s). Social interactions can be differentiated into accidental, repeated, regular, and regulated. Social interactions form the basis for social relations.


In statistics, an interaction is a term in a statistical model in which the effect of two, or more, variables is not simply additive.

An example from statistics applied to psychology

If we were examining the effect of two variables, sex and premature birth, on health outcomes we would describe any difference in health outcome scores between sexes as a main effect. Similarly any difference in scores of full term/premature birth would be described as a main effect. The presence of an interaction effect implies that the effect of sex on health outcome varies as a function of premature birth status.

Genetic interactions

Geneticists work with a number of different genetic interaction modes to characterize how the combination of two mutations affect (or does not affect) the phenotype: noninteractive, synthetic, asynthetic, suppressive, epistatic, conditional, additive, single-nonmonotonic and double-nonmonotonic. Further characterizations is enhancement interaction and nonadditive interaction.

The word epistasis is also used for genetic interaction in some contexts.

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