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Calculating the attractive or repulsive force between two magnets is, in the general case, a very complex operation, as it depends on the shape, magnetization, orientation and separation of the magnets. The magnetic pole model does depend on some knowledge of how the ‘magnetic charge’ is distributed over the magnetic poles.
If two charges have the same sign, the electrostatic force between them is repulsive; if they have different sign, the force between them is attractive. An electric field is a vector field that associates to each point in space the Coulomb force experienced by a unit test charge . [ 19 ]
The electrostatic field (lines with arrows) of a nearby positive charge (+) causes the mobile charges in conductive objects to separate due to electrostatic induction. Negative charges (blue) are attracted and move to the surface of the object facing the external charge. Positive charges (red) are repelled and move to the surface facing away ...
Diamagnetism is a quantum mechanical effect that occurs in all materials; when it is the only contribution to the magnetism, the material is called diamagnetic. In paramagnetic and ferromagnetic substances, the weak diamagnetic force is overcome by the attractive force of magnetic dipoles in the material.
A positive value of U is due to a repulsive force, so interacting particles are at higher energy levels as they get closer. A negative potential energy indicates a bound state (due to an attractive force). The Coulomb barrier increases with the atomic numbers (i.e. the number of protons) of the colliding nuclei:
where A is the Hamaker coefficient, which is a constant (~10 −19 − 10 −20 J) that depends on the material properties (it can be positive or negative in sign depending on the intervening medium), and z is the center-to-center distance; i.e., the sum of R 1, R 2, and r (the distance between the surfaces): = + +.
In the image, the vector F 1 is the force experienced by q 1, and the vector F 2 is the force experienced by q 2. When q 1 q 2 > 0, the forces are repulsive (as in the image) and when q 1 q 2 < 0 the forces are attractive (opposite to the image). The magnitude of the forces will always be equal.
At a given temperature and pressure, repulsive forces tend to make the volume larger than for an ideal gas; when these forces dominate Z is greater than unity. When attractive forces dominate, Z is less than unity. The relative importance of attractive forces decreases as temperature increases (see effect on gases).