International System of Units

Examples of International System of Units in the following topics:

• Prefixes and Other Systems of Units

  • Today, the prefixes are standardized for use in the International System of Units (SI) by the International Bureau of Weights and Measures.There are twenty prefixes officially specified by SI .
  • The SI Unit system, or the metric system, is used by the majority of countries in the world, and is the standard system agreed upon by scientists and mathematicians.
  • Colloquially, however, other systems of units are used in many countries.
  • Some units that are widely used are not a part of the International System of Units and are considered Non-SI Units.
  • The twenty prefixes officially specified by the International System of Units

• Standard Units (SI Units)

  • The International System of Units (abbreviated SI) is the metric system used in science, industry, and medicine.
  • The International System of Units (abbreviated SI, from the French Système international d'unités) is the metric system used in science, industry, and medicine.
  • The SI units of measurement have an interesting history.
  • Causey teaches scientific units of the SI system, the metric system, and the CGS system.
  • Science measurements are based on the metric system, so it is important that you know the metric base units and prefixes.

• Absolute Temperature

  • Absolute temperature is the most commoly used thermodyanmic temperature unit and is the standard unit of temperature.
  • Therefore, it is reasonable to choose absolute zero, where all classical motion ceases, as the reference point (T=0) of our temperature system .
  • By using the absolute temperature scale (Kelvin system), which is the most commonly used thermodynamic temperature, we have shown that the average translational kinetic energy (KE) of a particle in a gas has a simple relationship to the temperature:
  • It is one of the seven base units in the International System of Units (SI) and is assigned the unit symbol K.
  • By international agreement, the unit kelvin and its scale are defined by two points: absolute zero and the triple point of Vienna Standard Mean Ocean Water (water with a specified blend of hydrogen and oxygen isotopes).

• Length

  • Length is a physical measurement of distance that is fundamentally measured in the SI unit of a meter.
  • Many different units of length are used around the world.
  • In the United States, the U.S. customary units operationally describe length in terms of the basic unit of an inch.
  • As such, a standard unit of measurement that is internationally accepted is needed.
  • The basic unit of length as identified by the International System of Units (SI) is the meter.

• Mass

  • Mass is a physical property of matter that depends on size and shape of matter, and is expressed as kilograms by the SI system.
  • Weight is a different property of matter that, while related to mass, is not mass, but rather the amount of gravitational force acting on a given body of matter.
  • This relation is called a unit.
  • The International System of Units (SI) measures mass in kilograms, or kg.
  • There are other units of mass, including the following (only the first two are accepted by the SI system):

• SI Units of Pressure

  • The International System of Units (abbreviated SI from the French Système International d'Unités) is the basis of the metric system.
  • Pressure, the effect of a force applied to a surface, is a derived unit.
  • The unit of pressure in the SI system is the pascal (Pa), defined as the force of one newton per square meter:
  • Another unit of pressure used in meteorology is the bar:
  • A prefix may be added to a unit's name to describe a multiple of the original unit.

• Length

  • In most systems of measurement, the unit of length is a fundamental unit, from which other units are defined.
  • One of the oldest units of length measurement used in the ancient world was the 'cubit,' which was the length of the arm from the tip of the finger to the elbow.
  • In the physical sciences and engineering, when one speaks of "units of length", the word "length" is synonymous with "distance".
  • Units of length may be based on lengths of human body parts, the distance traveled in a number of paces, the distance between landmarks or places on the Earth, or arbitrarily on the length of some fixed object.In the International System of Units (SI), the basic unit of length is the meter and is now defined in terms of the speed of light.
  • In U.S. customary units, English or Imperial system of units, commonly used units of length are the inch, the foot, the yard, and the mile.

• Converting from One Unit to Another

  • Using physical laws, units of quantities can be expressed as combinations of units of other quantities.
  • Derived units are a matter of convenience, as they can be expressed in terms of basic units.
  • Different systems of units are based on different choices of base units.
  • The most widely used system of units is the International System of Units, or SI.
  • Derived units are based on units from the SI system of units.

• Time

  • Time is the fundamental physical quantity of duration and is measured by the SI Unit known as the second.
  • Time is one of the seven fundamental physical quantities in the International System (SI) of Units.
  • An operational definition of time is highly useful in the conduct of both advanced experiments and everyday affairs of life.
  • Periodic events and motion have long served as standards for units of time.
  • Today, the SI Unit of the second is defined in terms of radiation emitted by cesium atoms.

• Mass

  • The SI unit of mass is the kilogram (kg).
  • The kilogram is defined as being equal to the mass of the International Prototype Kilogram (IPK), which is almost exactly equal to the mass of one liter of water.
  • Four of the seven base units in the SI system are defined relative to the kilogram, so the stability of this measurement is crucial for accurate and consistent measurements.
  • In 2005, the International Committee for Weights and Measures (CIPM) recommended that the kilogram be redefined in terms of a fundamental constant of nature, due to evidence that the International Prototype Kilogram will vary in mass over time .
  • This value, though given in kilograms, is actually the non-SI unit of measure known as the kilogram-force.