Name: weightlessness and einstein’s equivalence
Uploaded: 2023-04-30T11:07:46.000Z
Duration: 1 min 18 s
Channel: JoVE

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Physics

PH.9

PH.9.c

Principle of Equivalence

Una navetta spaziale in orbita attorno alla Terra è in caduta libera, vincolata dalla forza gravitazionale terrestre. Tuttavia, un astronauta all'interno dello space shuttle si sente senza peso, come se nessuna forza agisse su di lui.
Supponiamo che lo Space Shuttle acceleri verso l'alto a 9,8 m/s2; il pavimento della sala dello Space Shuttle si sposterà verso l'astronauta fluttuante. Tuttavia, all'astronauta, sembra che stia accelerando verso il basso verso il pavimento dello Space Shuttle a 9,8 m/s2.
Per lui, l'accelerazione crea un'attrazione nello space shuttle, simile alla gravità sulla superficie terrestre. Seduto all'interno della stanza chiusa dello Space Shuttle, l'astronauta non è in grado di distinguere se si trova sulla Terra o sta accelerando nello spazio.
Einstein, quindi, affermò che non c'è differenza tra un campo gravitazionale uniforme e un'accelerazione uniforme in assenza di gravità. Questo è noto come Principio di Equivalenza.
Concluse che la gravità non è una forza tra due masse, ma emerge dall'interazione tra materia e spazio.

il principio di equivalenza

Stando ad Albert Einstein (1897 – 1955), la caduta libera e il sentirsi senza peso sono intrinsecamente collegati. Se una persona è in caduta libera sotto la gravità, per esempio, tuffandosi verso la Terra da un aeroplano, essa si sentirebbe completamente senza peso. Allo stesso modo, una persona che scende in un ascensore potrebbe sentirsi parzialmente priva di peso. In generale, si presume che un oggetto in un campo gravitazionale uniforme e un oggetto che sottostà ad accelerazione costante in assenza di gravità e sotto le stesse condizioni sperimentali (cioè, nessun esperimento può differenziare i due scenari). Questa affermazione è chiamata principio di equivalenza.

Il principio indirizza ad un presupposto fondamentale della legge di gravitazione universale di Newton: le masse che determinano la forza gravitazionale di attrazione tra due oggetti sono supposte essere le stesse masse che determinano la loro reazione alle forze attraverso le leggi del movimento di Newton. Comunque, queste due masse, qualche volta chiamate massa gravitazionale e massa inerziale, possono essere differenti nella pratica. Le conseguenze del presupporre che esse siano uguali, e così i risultati della combinazione della legge di gravitazione universale di Newton con le leggi del movimento di Newton, concordano con gli esperimenti. In altre parole, il presupposto risulta essere sperimentalmente valido. Tuttavia, la ragione di questa conseguenza non è compresa.

Stando al principio di equivalenza, questa non è una coincidenza. Fondamentalmente, l'accelerazione uniforme e la gravità sono uguali.

Mettendo in relazione l'accelerazione uniforme con la gravitazione, Einstein propose che la gravitazione non sia una forza tra due oggetti. Invece, essa è un effetto dei due oggetti in uno spazio-tempo intorno ad essi, il quale a sua volta determina le loro dinamiche. Egli ebbe queste idee matematiche nella sua teoria generale della relatività nel 1915.

Questo testo è adattato da <a href="https://openstax.org/books/university-physics-volume-1/pages/13-7-einsteins-theory-of-gravity">Openstax, University Physics Volume 1, Section 13.7: Einstein's Theory of Gravity.</a>

Il principio di equivalenza

Secondo Albert Einstein (1897-1955), la caduta libera e la sensazione di assenza di peso sono intrinsecamente legate. Se una persona fosse in caduta libera sotto la gravità, per ...

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weightlessness and einstein’s equivalence

Weightlessness and Einstein’s equivalence principle are closely connected in gravity. A person in free fall under gravity, such as someone diving toward Earth from an airplane, would feel completely weightless. A person descending in a lift may feel partially weightless.

The principle of equivalence says that an object in a uniform gravitational field and an object accelerating at a constant rate with no gravity are under the same experimental conditions. In other words, no experiment can tell the two situations apart. This idea links gravity with uniform acceleration.

The principle also addresses a key assumption in Newton’s law of gravitation. It assumes that the mass that creates gravitational attraction is the same as the mass that responds to force in Newton’s laws of motion. These are sometimes called gravitational mass and inertial mass. They can be different in practice, but the results from combining Newton’s law of gravitation with Newton’s laws of motion still match experiments.

Einstein argued that this agreement is not a coincidence. He proposed that gravitation is not simply a force between two objects. Instead, it is an effect of those objects on the space-time around them, which then shapes their motion. He turned these ideas into mathematics in his general theory of relativity in 1915.

Weightlessness and Einstein’s Equivalence

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Weightlessness and Einstein’s equivalence principle are closely connected in gravity. A person in free fall under gravity, such as someone diving toward Earth from an airplane, would feel completely weightless. A person descending in a lift may feel partially weightless. The principle of equivalence says that an object in a uniform gravitational field and an object accelerating at a constant rate with no gravity are under the same experimental conditions. In other words, no experiment can tell...

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Learn how free fall, weightlessness, and constant acceleration connect in Einstein’s equivalence principle and why it led to general relativity.

Weightlessness and Einstein’s Equivalence | JoVE K12

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Weightlessness and Einstein’s Equivalence

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