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

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


upthrust
You can ascend

Overhead push. This term is often used to refer to the upward thrust exerted on a body submerged, wholly or partially, in a fluid medium. The reason for this force is the pressure difference between the upper and lower levels.
See Archimedes principle.
This upward thrust makes objects easier to carry under water than in the air. It is the force that causes ships and balloons to float.


uranium
uranium m

Uranium. The most massive (heaviest) natural element found on Earth. Uranium is a metal with 92 proton numbers. Uranium has three isotopes, which are shown in the table below. All three isotopes are radioactive as sources of the alpha particle.
Uranium 235U is fissile - a nucleus can split when it absorbs neutrons.
Because each fission results in the appearance of several other neutrons, a chain reaction can occur, which is the basis of nuclear power and the atom bomb.



Analog -------------- A ----- N ---- Z

Uranium 234 --- 142 ---- 92 - 234 -

Uranium 235----143 ---- 92 - 235 -

Uranium 238---146----92 - 238--


Year T1/2

105 x 3
108 x 7
109 x 5

Abundance

% 0.006
% 0.7
% 99.3

In the table, Z is the number of protons, N is the number of neutrons, A is the nuclear number, and T1/2 is the half-life period.

It is common to “enrich” pure uranium, whether for use as fuel or as a bomb, which means increasing the percentage of 235U in it several times its normal percentage of 0.7%.