In the theory of relativity, four-acceleration is a four-vector (vector in four-dimensional spacetime) that is analogous to classical acceleration (a three-dimensional vector, see three-acceleration in special relativity). Four-acceleration has applications in areas such as the annihilation of antiprotons, resonance of strange particles and radiation of an accelerated charge.
In inertial coordinates in special relativity, four-acceleration is defined as the rate of change in four-velocity with respect to the particle's proper time along its worldline. We can say:
where
with the three-acceleration and the three-velocity, and
and
is the Lorentz factor for the speed (with ). A dot above a variable indicates a derivative with respect to the coordinate time in a given reference frame, not the proper time (in other terms, ).
In an instantaneously co-moving inertial reference frame , and , i.e. in such a reference frame
Geometrically, four-acceleration is a curvature vector of a worldline.
Therefore, the magnitude of the four-acceleration (which is an invariant scalar) is equal to the proper acceleration that a moving particle "feels" moving along a worldline. A worldline having constant four-acceleration is a Minkowski-circle i.e. hyperbola (see hyperbolic motion)
The scalar product of a particle's four-velocity and its four-acceleration is always 0.
Even at relativistic speeds four-acceleration is related to the four-force: where m is the invariant mass of a particle.
When the four-force is zero, only gravitation affects the trajectory of a particle, and the four-vector equivalent of Newton's second law above reduces to the geodesic equation. The four-acceleration of a particle executing geodesic motion is zero. This corresponds to gravity not being a force. Four-acceleration is different from what we understand by acceleration as defined in Newtonian physics, where gravity is treated as a force.
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In the special theory of relativity, four-force is a four-vector that replaces the classical force. The four-force is defined as the rate of change in the four-momentum of a particle with respect to the particle's proper time: For a particle of constant invariant mass , where is the four-velocity, so we can relate the four-force with the four-acceleration as in Newton's second law: Here and where , and are 3-space vectors describing the velocity, the momentum of the particle and the force acting on it respectively.
En physique, en particulier en relativité restreinte et en relativité générale, la quadrivitesse d'un objet est un quadrivecteur généralisant le vecteur vitesse en mécanique classique. La quadrivitesse est une des notions que le mathématicien et physicien allemand Hermann Minkowski (-) a introduites dans le cadre de sa reformulation géométrique de la relativité restreinte d'Albert Einstein (-). La quadrivitesse est ainsi désignée car elle est le quadrivecteur qui généralise la notion de vitesse de la mécanique newtonienne.
In the theory of relativity, four-acceleration is a four-vector (vector in four-dimensional spacetime) that is analogous to classical acceleration (a three-dimensional vector, see three-acceleration in special relativity). Four-acceleration has applications in areas such as the annihilation of antiprotons, resonance of strange particles and radiation of an accelerated charge. In inertial coordinates in special relativity, four-acceleration is defined as the rate of change in four-velocity with respect to the particle's proper time along its worldline.
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