Group items tagged

Jusqu'en 1950, le magnétisme terrestre semblait être un heureux accident de la nature.  Beaucoup de facteurs devaient converger pour le maintenir : le noyau fluide de la Terre, sa conductivité électrique et ses mouvements, le tout doit obéir à des critères bien stricts de la théorie de la dynamo.  Nous savons maitenant que Vénus est la seule planète qui n'a pas de magnétisme. Les planètes diffèrent beaucoup entre elles en taille et en propriétés, ainsi que par leurs champs .  Les planètes ont toutes un champ magnétique ou en ont eu un dans le passé (tels Mars et la Lune). 

"Qu'est-ce-que cet objet brillant là-haut?" .  C'était Jupiter, le signal provenait de cette planète.  En publiant leurs résultats, les deux astronomes proposèrent que " la cause de cette radiation non-connue était sans doute dûe à des perturbations électriques dans l'atmosphère de Jupiter".

Ces quatre planètes ont un champ magnétique plus fort que la Terre

Planck Units

Planck units are largely based upon three fundamental units, h, G, and c.

The gravitational constant is given the symbol "G".   It is a measured value used in the force equation for gravity (see below). F = Gm1m2 / r2 The m units are masses of two bodies which are separated by a distance r.   By rearranging the equation, we have G (see below). G = Fr2 / m1m2 The gravitational force, F, was measured between two masses to arrive at G.   At various times, the laboratory equipment and methods were improved to arrive at more accurate values for G.   The physics texts were not usually updated for the new values because (1) the changes were not great enough to justify the added expense to the texts, and (2) the changes were happening frequently enough to make each text obsolete before it arrived in the hands of students.   Consequently, there are numerous variations of G to be found, but the differences between them are slight. There are many systems of weights and measures used in physics.   Fundamental constants such as G often have two values according to the measuring system used.   When two such units are mixed to arrive at subsidiary units such as the planck length, the result is a completely erroneous value along with units of measure which do not apply.   Consequently, it is important to convert the various units of the fundamental constants used to the same system of units.   In may instances of late, this has not been done. Finally, there is human error involved in copying from an old text to create a new next.   This means that it is wise to check various texts to see if they all agree (they usually don't), and decide what is correct and what is not correct.   For G, the following was discovered.