Instrument for measuring the viscosity (resistance to internal
flow) of a fluid. In one type, the time taken for a given volume
of fluid to flow through an opening is recorded. In the
capillary-tube viscometer, the pressure needed to force the
fluid to flow at a specified rate through a narrow tube is
measured. Other types depend on measurements of the time taken
for a sphere to fall through the fluid, or of the force needed
to rotate the inner cylinder of a pair (the space between the
two cylinders being filled with the fluid under test), or of the
rate at which oscillations of a disk vibrating in the fluid die
out. Learn more about viscometer with a free trial on
Britannica.com. In general, either the fluid remains stationary
and an object moves through it, or the object is stationary and
the fluid moves past it. The drag caused by relative motion of
the fluid and a surface is a measure of the viscosity. The flow
conditions must have a sufficiently small value of Reynolds
number for there to be laminar flow