Van derWaals’ force is the weak attractive force between two molecules which arises from electric dipole interactions. It can lead to the formation of stable but weakly bound dimer molecules or clusters. They are named after the Dutch physicist Johannes van der Waals (1837-1923).
Van der Waals’s radius is one half the distances between two nonbonded atoms, when attractive and repulsive forces between the atoms are balanced.
Van der Waals’ equation is an equation of state for real fluids which takes the form:
where p is pressure, Vm is molar volume, T is temperature, R is the molar gas constant, and a and b are characteristic parameters of the substance which describe the effect of attractive and repulsive intermolecular forces.
Centrifugal force is a force which moves a body away from the centre of motion.
Centripetal force is a force which makes body move through a curvature. Its orientation is always in path forwards the centre of rotation.
Electromotive force (e.m.f. or EMF) is the difference in electric potential that exists between two dissimilar electrodes immersed in the same electrolyte or otherwise connected by ionic conductors.
London’s force is an intermolecular attractive force that arises from a cooperative oscillation of electron clouds on a collection of molecules at close range.
Air stripping is a process for the removal of volatile organic contaminants from groundwater. The groundwater flows downward inside a tower filled with materials (the packing) over a large surface area. Air is introduced at the bottom of the tower and is forced upward past the falling water. The volatiles evaporate from the water and are collected in air filters or released to the atmosphere.
Ampere (A) is the SI base unit of electric current.
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2×10-7 newton per metre of length.
Analytical balances are instruments used for precise determining mass of matter. Analytical balances are sensitive and expensive instruments, and upon their accuracy and precision the accuracy of analysis result depends. The most widely used type of analytical balances are balances with a capacity of 100 g and a sensitivity of 0.1 mg. Not one quantitative chemical analysis is possible without usage of balances, because, regardless of which analytical method is being used, there is always a need for weighing a sample for analysis and the necessary quantity of reagents for solution preparation.
The working part of the balance is enclosed in a glass-fitted case. The baseplate is usually of black glass or black slate. The beam has agate knife-edges at its extremes, supporting stirrups from which balance pans are suspended. Another agate or steel knife-edge is fixed exactly in the middle of the beam on its bottom side. This knife-edge faces downwards and supports the beam. When not in use and during loading or unloading of the pans, the balance should be arrested.
The principle of operation of a modern laboratory balance bears some resemblance to its predecessor - the equal arm balance. The older instrument opposed the torque exerted by an unknown mass on one side of a pivot to that of an adjustable known weight on the other side. When the pointer returned to the center position, the torques must be equal, and the weight was determined by the position of the moving weights.
Modern electronic laboratory balances work on the principle of magnetic force restoration. In this system, the force exerted by the object being weighed is lifted by an electromagnet. A detector measures the current required to oppose the downward motion of the weight in the magnetic field.
Generalic, Eni. "Van der Waals%E2%80%99 force." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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