1u = 1.66 x 10 -27 kg.Ī unit of measurement, equal to the number of electrons surrounding a neutral (uncharged) atom, and also to the number of protons in the nucleus. Since 1960 the unified atomic mass unit has been defined as 1/12 the mass of the carbon-12 atom. Originally these relative masses were based on hydrogen, known to be the lightest element, having a mass of 1 u, and all the other atoms should have masses which are whole-number multiples of this (then unknown) mass of the hydrogen atom. The unit of mass used for measuring the masses of atoms and molecules. One atmosphere is equal to 1.013 25 bar or 1.013 25 x 10 5 Pa or 760 mmHg. This unit is accepted for use with SI units.Ī unit of pressure equal the average pressure of the Earth's atmosphere at sea level. The astronomical unit is a convenient yardstick for measuring the distances between objects in the Solar System. The currently accepted value is 1.495 978 x 10 11 metre or about 92 955 807 miles. One astronomical unit equals the average distance from the centre of the Earth to the centre of the Sun. The SI defines s as the symbol for the time unit and recommends " as the symbol for the arcsecond.Īn old unit of area equal to 100 square metre.Īstronomical unit (ua or au or AU) convertĪ unit of distance used by astronomers to measure distances in the Solar System. Care is needed not to confuse symbols with units of length or time. One arcsecond is a very small angle: there are 1 296 000 seconds in a circle. The SI recommends ' as the symbol for arcminute.Ī unit of angle measure, also called the second of arc, equal to 1/60 arcminute. Angstrom unit named after the Swedish physicist Anders Jon Ångström (1814-1874) and is used most often to measure extremely small lengths like the wave length of light.Ī unit of angle measurement, also called the minute of arc, equal to 60 arcseconds and to 1/60 degree. The SI derived unit of magnetic field strength.Ī metric unit of length, equal to 0.1 nanometre or 10 -10 metre. This is equivalent to exactly 3600 coulomb. One ampere hour is the charge accumulated by a steady flow of one ampere for one hour. The ampere is defined as the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 x 10 -7 newton per metre of length.Ī unit of electric charge often used to state the capacity of a battery. The SI base unit of electric current, named after the French physicist André-Marie Ampère (1775-1836). One acre is equal to 0.404 687 3 hectare. In metric the unit corresponding to the acre is the hectare, which is 10,000 square metre. The acre was defined as the area of a field one furlong long by 1/10 furlong wide. The acre (old English word meaning field) was originally defined as the area that could be plowed in a day by a yoke of oxen. Īn old unit of area used for measuring the area of land. The A to Z hyperlinks may assist in finding that unit of measurement.Ī B C D E F G H I J K L M N O P Q R S T U V W X Y Z The following glossary of SI units and other units is far from complete, but does cover the main units used today and all the units used on this web site.
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