أكاديميا - كولنز - معاجم الجيب العلمية - الفيزياء - انكليزي - فرنسي - عربي الحرف ٢_ a

Academia - Collins - Pocket Scientific Dictionaries - Physics - English - French - Arabic - Letter 2_ A


acoustics
acoustic f

Audios. Specifications of a building or space in terms of
His response to sound.

action. action
action f

an act . The word stopped being used means force.


adhesion
adhésion f

adhesion. One of the categories of the kinematic model of matter says that particles of matter tend to attract each other. Adhesion is the attraction between particles of different materials. For example, adhesion between water particles and glass causes the meniscus shown below:

Glass tube
My hair rises
Crescent surface
water

See also surface, capillarity, cohesion, and tension.

air pressure
Expression of air

air pressure . Pressure at a point in the atmosphere. The force exerted on a square meter at any level is equal to the weight of the air above this square meter. Thus, air pressure decreases at high altitudes. As a result, simple altimeters measure height as a form of barometer (which measures air pressure).

low pressure
air
High pressure
The earth's surface
Air pressure decreases with increasing altitude (scale drawing).

The standard value of air pressure at the Earth's surface is about 100 kilopascals, or 760 mm of mercury. The actual value varies from one place to another and from one hour to another depending on the weather. Because changes in air pressure indicate changes in the weather, barometers are of great benefit in weather forecasting.

alphadecay
Designation of alpha

Alpha decay: This decay occurs when certain radioactive isotopes decay, releasing an alpha particle. As a result, the number of protons decreases by two protons. Example:

226/88Ra > 222/86Rn + 4/2He + Energy 88 86
The 4/2He nucleus here is an alpha particle.


alpha particle (a)
particle f alpha

Alpha particle. This particle consists of two neutrons and two protons that are linked together and thus form the nucleus of a helium atom. Many radioactive nuclei release alpha particles when they decay. An example of this is the common uranium isotope 238/92U:

238/92U > 234/90Th + 4/2a + power

The energy transferred is shown as kinetic energy of the alpha particle. When this particle collides with other particles, its speed slows down, and there is a transfer of energy to the material, which leads to a small increase in temperature. The flow of alpha particles from a radioactive source is called alpha radiation. This radiation carries a positive charge and energy from the source. But matter slows it down quickly, and therefore its range is very short, and does not exceed a few centimeters in the air, for example.

The loss of alpha radiation in matter leads to the appearance of ions.
See atomic radiation detector radiatons.

alternating current (AC)
Courant m alternif

Alternating current is a current whose value varies uniformly around zero. Just as the term covers the pure sine waveforms in Figure (a) below, it also covers the two currents in cases (b) and (c). See interference. The wave in Figure (d) shows an alternating current added to a direct current.

The frequency of main lines in Britain is 50 Hz (cycles per second). Note that many people use the term alternating current (AC) loosely. For example, they may talk about alternating current voltage instead of alternating voltage.
See also rectifier.

alternator
alternateur m

Rep. See generators.