1. THE LAW OF UNIVERSAL GRAVITATION
Legend has it that the idea of \u200b\u200bthe law of gravity comes to Newton watching an apple fall from a tree (other versions give the apple fall directly on his head), Newton would asked what would happen if the apple had fallen from a height equal to the distanza tra la luna e la terra. Si accorse dunque che la mela e la luna, questi due oggetti così diversi tra loro, potevano ugualmente essere soggetti alla stessa legge fisica. In realtà la formulazione della legge di gravità è l'ultimo atto di un lungo percorso scientifico che aveva portato numerosi fisici prima di Newton ad analizzare solo parzialmente le leggi della dinamica dei corpi a seguito delle scoperte di Galileo .
Newton scoprì che le masse dei corpi celesti si attraggono proporzionalmente al prodotto delle masse e in ragione inversa del quadrato delle distanze, tale attrazione prese il nome di gravità. Questa legge, semplice in sé, comportava una rivoluzione epocale nella meccanica dei corpi, la gravità was universally valid in all places of the universe and suggested a reciprocal relationship and mutual influence of all bodies in the cosmos. Gravity is the force that a body on the ground is still held to the ground. More mass, the greater will be its gravitational pull, and nothing that has a mass less may be released by the gravitational pull of the greatest mass, except with great effort (think of the enormous amount of energy needed to detach from ground rockets and let them escape the Earth's gravity). In light of the new theory, the elliptical motion of the stars of Kepler was questioned, since the ellipses describing the Earth around the Sun could not be sustained as perfect as the study of Kepler, but he should submit to the influence of disturbances resulting from the mass of other planets.
The universe described by Newton possessed the quality of being uniform in an absolute sense. This means that each region of space-time universe is not only subject to the same physical laws, but also had a level playing time and geometric space and time which will then be put into question the theory of relativity. The classical physics of Newton still involved the necessary presence of the ether, the presence of a light material that was still volatile and almost occupy all spaces of the cosmos to make possible the transmission of physical and mechanical causes and effects of all phenomena (the story of the refutation of the ether see Einstein's relativity ).
2. Mass and Weight
The definition of the law of gravity implies the distinction between mass and weight of a body: the mass of a body is the amount of matter present in the body, according to the quantity which forms the force of gravity and the weight Instead of a body is the result of the gravitational force applied on the body. The farther away from Earth, which is the largest agglomeration of matter "in the immediate vicinity" of man, the strength of gravity exerted by the planet on the bodies decreases, which is why astronauts have envy gift of weight loss and soaring into space. The mass is then quell'agglomerato of matter that makes it possible for gravity to exert a certain force of attraction, and the weight is simply the effect of this force (on the moon, the bodies are lighter because it is less mass to attract If the bodies in a more bland).
Again, as already seen for Galileo, the new scientific method not only allows you to reach conclusions that go beyond common sense, but also allows to predict the behavior of extraordinary bodies in unexplored regions of space (the astronauts necessarily suffer the effects of that law of gravity was discovered that the first three centuries of their experiences in weightlessness).
EMANUELE GRAMAGLIA.
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