torr
Noun: A unit of pressure equal to exactly 1/760 of a standard atmosphere, or approximately 133.322 pascals. It is a non-SI unit named after the Italian physicist Evangelista Torricelli, who invented the barometer.
The torr is primarily used in scientific contexts, especially in vacuum physics, engineering, and chemistry, to measure low pressures or pressure differences. It is very close in value to the traditional millimeter of mercury (mmHg).
Scientific Measurement:
- The vacuum chamber was evacuated to a pressure of 10^-3 torr.
- Blood pressure is often reported in millimeters of mercury, a unit almost identical to the torr.
Definition and Comparison:
- One standard atmosphere is defined as exactly 760 torr.
- The conversion factor is 1 torr ≈ 133.322 pascals.
- "torr" as a Named Unit: The word is always written in lowercase, even though it is derived from a proper name (Torricelli). The plural is "torr" (e.g., 50 torr).
- Technical Contexts: It is commonly used with metric prefixes, such as (mTorr) for very low vacuum pressures.
- Millimeter of mercury (mmHg): A nearly equivalent unit of pressure based on the height of a mercury column. For most practical purposes, 1 mmHg = 1 torr.
- Pascal (Pa): The SI unit of pressure. 1 torr = 133.322 Pa.
- Atmosphere (atm): A standard unit of pressure. 1 atm = 760 torr.
- Bar: Another unit of pressure. 1 bar ≈ 750.062 torr.
- Millimeter of mercury (mmHg): (For most practical intents and purposes, these are interchangeable, though their technical definitions are slightly different.)
The torr represents a specific, standardized amount of pressure. Its key characteristic is its direct link to atmospheric pressure (1/760th of an atmosphere) and its historical link to mercury-column barometers. It is not used for everyday atmospheric pressure reporting (which uses hectopascals or inches of mercury) but is standard in many technical fields.
- a unit of pressure equal to 0.001316 atmosphere; named after Torricelli