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

K12 Standards

Virginia  Standards of Learning

HIgh School

Physics

PH.9

PH.9.c

Principle of Equivalence

Une navette spatiale en orbite autour de la Terre est en chute libre, liée par la force gravitationnelle de la Terre. Cependant, un astronaute à l’intérieur de la navette spatiale ressent l’apesanteur, comme si aucune force n’agissait sur lui.
Supposons que la navette spatiale accélère vers le haut à 9,8 m/s2 ; le sol de la salle de la navette spatiale se déplacera vers l’astronaute flottant. Cependant, pour l’astronaute, il semble qu’il accélère vers le sol de la navette spatiale à 9,8 m/s2.
Pour lui, l'accélération crée une attraction dans la navette spatiale, similaire à la gravité à la surface de la Terre. Assis à l’intérieur de la salle fermée de la navette spatiale, l’astronaute ne peut pas distinguer s’il est sur Terre ou s’il accélère dans l’espace.
Einstein a donc déclaré qu’il n’y a pas de différence entre un champ gravitationnel uniforme et une accélération uniforme en l’absence de gravité. C’est ce qu’on appelle le principe d’équivalence.
Il a conclu que la gravité n’est pas une force entre deux masses, mais qu’elle émerge de l’interaction de la matière et de l’espace.

principe d'équivalence

Selon Albert Einstein (1897-1955), la sensation de chute libre et de poids nul sont intrinsèquement liées. Par exemple, si une personne est en chute libre sous l'effet de la gravité, en plongeant vers la Terre depuis un avion, elle se sentirait complètement sans poids. De même, une personne qui descend dans un ascenseur peut se sentir partiellement sans poids. De manière générale, on suppose qu'un objet dans un champ gravitationnel uniforme et un objet soumis à une accélération constante en l'absence de gravité se trouvent dans les mêmes conditions expérimentales (c'est-à-dire qu'aucune expérience ne peut faire la différence entre les deux scénarios). Cette affirmation est appelée le principe d'équivalence.

Le principe aborde une hypothèse fondamentale de la loi de gravitation de Newton : les masses qui déterminent la force d'attraction gravitationnelle entre deux objets sont supposées être les mêmes masses qui déterminent leur réaction aux forces via les lois du mouvement de Newton. Cependant, ces deux masses, parfois appelées masse gravitationnelle et masse inertielle, peuvent être différentes en pratique. Les conséquences de les considérer comme identiques et donc les résultats de la combinaison de la loi de gravitation de Newton avec les lois du mouvement de Newton sont en accord avec les expériences. En d'autres termes, l'hypothèse s'avère être valide expérimentalement. Cependant, la raison de cette conséquence n'est pas comprise.

Selon le principe d'équivalence, ce n'est pas une coïncidence. Fondamentalement, l'accélération uniforme et la gravitation sont les mêmes.

En établissant un lien entre l'accélération uniforme et la gravitation, Einstein a proposé que la gravitation n'est pas une force entre deux objets. Au contraire, c'est un effet des deux objets sur l'espace-temps qui les entoure, ce qui détermine à son tour leur dynamique. Il a exprimé ces idées mathématiquement dans sa théorie générale de la relativité en 1915.

Ce texte est adapté de <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>

Principe d'équivalence

Selon Albert Einstein (1897-1955), la chute libre et la sensation d’apesanteur sont intrinsèquement liées. Si une personne était en chute libre sous l’effet de la gravité, pour ...

Education

Enseignement

JoVE Core

Physique

Unit 1

Unité 1

Gravitation

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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

gravitation

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principle of 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...

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key terms and concepts

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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Earth and Space Science

Earth's Place in the Universe

9-12.ESS.1.3

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SC.912.E.5

SC.912.E.5.5

SC.912.E.5.10

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Astronomy

SAST4

SAST4.1

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PH.9.b

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PH.9.d

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PH.9.e

The student will investigate and understand that extremely large and extremely small quantities are not necessarily described by the same laws as those studied in Newtonian physics. Topics, such as these listed, may be included.

Weightlessness and Einstein’s Equivalence

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