# 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
. [more]
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. [How to read a Vernier]
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.