EarthWord – Viscosity

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Viscosity refers to a fluid’s resistance to flowing. Ever heard the phrase “slower than molasses?” Viscosity is what it’s referring to, since molasses has a fairly high viscosity and so doesn’t flow very quickly.

EarthWords is an on-going series in which we shed some light on the complicated, often difficult-to-pronounce language of science. Think of us as your terminology tour-guides, and meet us back here every week for a new word!

A USGS geologist collects a molten lava sample during a December 2015 lava flow from Puʻu ʻŌʻō.
A USGS geologist collects a molten lava sample during a December 2015 lava flow from Puʻu ʻŌʻō. As the lava cools on the surface, its viscosity increases and the flow slows down. Credit: USGS.

Definition:

  • Viscosity refers to a fluid’s resistance to flowing. Ever heard the phrase “slower than molasses?” Viscosity is what it’s referring to, since molasses has a fairly high viscosity and so doesn’t flow very quickly.

Etymology:

  • Speaking of molasses, viscosity comes from the Latin viscosus, which meant “sticky.”

Use/Significance in the Earth Science Community:

  • Viscosity is an important measurement in most studies of fluids, from water to oil. It affects how these liquids behave, and can change depending on such factors as temperature and pressure.

USGS Use:

  • Viscosity factors into USGS science in a number of ways. First, when studying the flow of lava and its effects, the viscosity of the flow can affect the speed at which the lava travels.
  • Next, in our water studies, the viscosity of both surface water and groundwater can affect all manner of things, from how fast a river flows to how deep groundwater can percolate.
  • Finally, viscosity is also a factor in our oil and gas research. In determining what types of oil and gas are present, as well as how much is technically recoverable, viscosity of the petroleum is very important.

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