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Academia - Collins - Pocket Scientific Dictionaries - Physics - English - French - Arabic - Letter 4_ A


Archimedes' principle
Principle m d'Archimede

Archimedes' principle. This principle relates to the upward driving force (upthrust) acting on any body that is fully or partially submerged in a fluid (liquid or gas). The upward thrust equals the weight of the displaced fluid. The reason here is due to the increase in pressure with increasing depth. Thus, the upward driving force resulting from pressure on the bottom of a submerged body is greater than the downward driving force resulting from pressure on the top of the body.

Each arrow here represents the amount of force exerted on a unit surface area of ​​the body and the resulting force
Facing upward.

If this upward driving force is similar to the body's weight, it floats. This is what gives the law of floatation: a floating body displaces an amount of fluid equal to its weight.


area(A)
aire f

space . Surface extension scale. The unit of measurement is the square meter (m2).

The following drawings show some simple shapes with...
Equations for calculating their areas.

Triangle A = 1/2h x b

Rectangle A = axb

Circle Α = π r2

Trapezium A = h x 1/2(a + b)

Cylinder A = 2π rxh

Ball Α = 4πχ r2


armature
induit m

Movement. An important part of an electrical device made of soft iron that is magnetized. This part may be the rotor in a motor, a generator, the moving plate in a bell, or a relay.


astrophysics
astrophysique f

Astrophysics. Studying the structure of the universe and how objects behave in it. It includes theories about the evolution of the universe, galaxies, stars, and planets. Astronomy provides the data used.


atmospheric pressure
Pressure atmospheric

Pressure . See air pressure.


atom
atome m

corn. One of the main particles of matter. It is the smallest particle in the element that can have the properties of the element. In a simple model of matter, atoms consist of a nucleus, a small mass of protons and neutrons surrounded by orbiting electrons. A proton or neutron is about 2000 times heavier
Electron.

Under normal circumstances, the atom does not have an electric charge, as it is neutral. If it has too few or too many negative electrons, it becomes an ion.


atom bomb
bombe f automatic

Atomic bomb. The design of nuclear weapons allows them to release huge amounts of energy in a small space
And a short time. This generates a long-range explosion and a fireball with a temperature exceeding one million degrees Celsius. Thus, these weapons have a terrifying destructive power, as they cause massive explosions and fires that cover very large areas.

The basic process in this bomb is the rapid reaction of fission (atomic bomb) or fusion (hydrogen bomb).
See also nuclear power and chain reaction.
In addition to the reaction giving a very large transfer of energy, it also produces many radioactive isotopes. These isotopes can attach to dust particles and travel with the wind over distances of hundreds of kilometers, producing a harmful “fallout” that may remain.
Falls have been a source of danger for many decades.


atomic mass unit (amu)
unit in automatic mass

Atomic mass unit. The mass of a proton is 1.66 x 10-24 grams.


atomic number
number m automatic

Atomic number. See proton number.