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J g is mass current density or mass flux (J g = ρ g v ρ, where v ρ is the velocity of the mass flow), with SI unit kg⋅m −2 ⋅s −1; J is electric current density; G is the gravitational constant; ε 0 is the vacuum permittivity; c is both the speed of propagation of gravity and the speed of light.
Electromagnetic forces are tremendously stronger than gravity, but tend to cancel out so that for astronomical-scale bodies, gravity dominates. Electrical and magnetic phenomena have been observed since ancient times, but it was only in the 19th century James Clerk Maxwell discovered that electricity and magnetism are two aspects of the same ...
The crucial new idea, for Einstein, was the introduction of a tetrad field, i.e., a set {X 1, X 2, X 3, X 4} of four vector fields defined on all of M such that for every p ∈ M the set {X 1 (p), X 2 (p), X 3 (p), X 4 (p)} is a basis of T p M, where T p M denotes the fiber over p of the tangent vector bundle TM.
Unification of theories about observable fundamental phenomena of nature is one of the primary goals of physics. [1] [2] [3] The two great unifications to date are Isaac Newton’s unification of gravity and astronomy, and James Clerk Maxwell’s unification of electromagnetism; the latter has been further unified with the concept of electroweak interaction.
Continuous charge distribution. The volume charge density ρ is the amount of charge per unit volume (cube), surface charge density σ is amount per unit surface area (circle) with outward unit normal nĚ‚, d is the dipole moment between two point charges, the volume density of these is the polarization density P.
In physics, gravity (from Latin gravitas 'weight' [1]) is a fundamental interaction primarily observed as mutual attraction between all things that have mass.Gravity is, by far, the weakest of the four fundamental interactions, approximately 10 38 times weaker than the strong interaction, 10 36 times weaker than the electromagnetic force and 10 29 times weaker than the weak interaction.
Although not normally considered a Scalar–Tensor theory of gravity, the 5 by 5 metric of Kaluza–Klein reduces to a 4 by 4 metric and a single scalar. So if the 5th element is treated as a scalar gravitational field instead of an electromagnetic field then Kaluza–Klein can be considered the progenitor of Scalar–Tensor theories of gravity.
Whereas gravity acts on all things that have mass, electromagnetism acts on all things that have electric charge. Furthermore, as there is the conservation of mass according to which mass cannot be created or destroyed, there is also the conservation of charge which means that the charge in a closed system (where no charges are leaving or ...