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In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. [1] The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point.
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 n̂, d is the dipole moment between two point charges, the volume density of these is the polarization density P.
This means that the time constant is the time elapsed after 63% of V max has been reached Setting for t = for the fall sets V(t) equal to 0.37V max, meaning that the time constant is the time elapsed after it has fallen to 37% of V max. The larger a time constant is, the slower the rise or fall of the potential of a neuron.
The center of mass of a body with an axis of symmetry and constant density must lie on this axis. Thus, the center of mass of a circular cylinder of constant density has its center of mass on the axis of the cylinder. In the same way, the center of mass of a spherically symmetric body of constant density is at the center of the sphere.
The resulting equation: ¨ = shows that the velocity = of the center of mass is constant, from which follows that the total momentum m 1 v 1 + m 2 v 2 is also constant (conservation of momentum). Hence, the position R ( t ) of the center of mass can be determined at all times from the initial positions and velocities.
The variable q is a constant multiple of the proper time τ for timelike orbits (which are traveled by massive particles), and is usually taken to be equal to it. For lightlike (or null) orbits (which are traveled by massless particles such as the photon ), the proper time is zero and, strictly speaking, cannot be used as the variable q .
In astronomy, the barycenter (or barycentre; from Ancient Greek βαρύς (barús) 'heavy' and κέντρον (kéntron) 'center') [1] is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit. A barycenter is a dynamical point, not a physical object.
It is the time required to charge the capacitor, through the resistor, from an initial charge voltage of zero to approximately 63.2% of the value of an applied DC voltage, or to discharge the capacitor through the same resistor to approximately 36.8% of its initial charge voltage.