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The simplest definition for a potential gradient F in one dimension is the following: [1] = = where ϕ(x) is some type of scalar potential and x is displacement (not distance) in the x direction, the subscripts label two different positions x 1, x 2, and potentials at those points, ϕ 1 = ϕ(x 1), ϕ 2 = ϕ(x 2).
The force can be written as the negative gradient of a potential, : =. Proof that these three conditions are equivalent when F is a force field Main article: Conservative vector field
In this case, the force can be defined as the negative of the vector gradient of the potential field. For example, gravity is a conservative force . The associated potential is the gravitational potential , often denoted by ϕ {\displaystyle \phi } or V {\displaystyle V} , corresponding to the energy per unit mass as a function of position.
The potential has units of energy per mass, e.g., J/kg in the MKS system. By convention, it is always negative where it is defined, and as x tends to infinity, it approaches zero. The gravitational field, and thus the acceleration of a small body in the space around the massive object, is the negative gradient of the gravitational potential ...
The same approach implies that the negative of the Laplacian of the gravitational potential is the mass distribution. Often the charge (or mass) distribution are given, and the associated potential is unknown. Finding the potential function subject to suitable boundary conditions is equivalent to solving Poisson's equation.
Geopotential is the potential of the Earth's gravity field.For convenience it is often defined as the negative of the potential energy per unit mass, so that the gravity vector is obtained as the gradient of the geopotential, without the negation.
The effective force, then, is the negative gradient of the effective potential: = = ^ where ^ denotes a unit vector in the radial direction. Important properties [ edit ]
This means that gravitational potential energy on a contour map is proportional to altitude. On a contour map, the two-dimensional negative gradient of the altitude is a two-dimensional vector field, whose vectors are always perpendicular to the contours and also perpendicular to the direction of gravity.