# Physics Glossary – V

Is a torus of energetic charged particles around Earth, trapped by Earth’s magnetic field. The presence of a radiation belt had been theorized prior to the Space Age and the belt’s presence was confirmed by the Explorer I on January 31, 1958 and Explorer III missions, under Doctor James Van Allen.

Van de Graaff Generator

Is a machine which uses a moving belt to accumulate very high charges on a hollow metal globe. The potential differences achieved in modern Van de Graaff generators can be up to 5 megavolts; applications for these exist with high voltage X-ray tubes and atom splitting experiments.

Van Der Waals Equations of State

Proposed in 1873, the van der Waals equation of state was one of the first to perform markedly better than the ideal gas law. In this landmark equation a is called the attraction parameter and b the repulsion parameter or the effective molecular volume. While the equation is definitely superior to the ideal gas law and does predict the formation of a liquid phase, the agreement with experimental data is limited for conditions where the liquid forms. It is now obsolete, now there are other Equations of state.

Velocity

Is a vector measurement of the rate and direction of motion. The scalar absolute value (magnitude) of velocity is speed

Vernier

Lets one read more precisely from a measurement scale. It was invented in the 1700s by a Frenchman named Vernier. A vernier has two scales, an “indicating” and a “data” scale. These move past each other, usually on a slide.

Viscosity

Is a property of fluids describing their internal resistance to flow and may be thought of as a measure of fluid friction. Rheology is the field of science that deals with viscosity; viscosity is measured with a viscometer.

Viscometer

Is an instrument used to measure the viscosity and flow parameters of a fluid. The common Brookfield-type viscometer determines the required force for rotating a disk in the fluid at known speed.

Voltaic Pile

It was invented by Alessandro Volta in 1800. He demonstrated that when certain metals and chemicals come into contact with each other they can produce an electrical current. He placed together several pairs of copper and zinc discs separated by paper soaked in salt water, and an electrical current was produced. This was the first chemical battery.

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