SI system

(noun)

A series of units that is accepted and used throughout the scientific world.

Related Terms

Examples of SI system in the following topics:

  • 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.
    • But in most of the world (including Europe) and in all scientific circles, the SI system is in common use.
    • The use of the SI system provides all scientists and engineers with a common language of measurement.
    • Causey teaches scientific units of the SI system, the metric system, and the CGS system.

  • SI Unit Prefixes

    • The basic SI units can be expressed as fractions and multiples of basic units by using a set of simple prefixes.
    • Now that we know about the SI system and what it provides to the scientist and engineer, we can examine some aspects of actual measurement.
    • The SI system utilizes a standard system of prefixes to the basic units that allow them to be more relevant to and descriptive of relative magnitude.
    • Briefly review the basic SI units before you study the prefixes.

  • SI Units of Pressure

    • The SI unit of pressure is the pascal (Pa), which is equal to one Newton per meter squared (N/m2).
    • The International System of Units (abbreviated SI from the French Système International d'Unités) is the basis of the metric system.
    • The SI was established in 1960 and is based on the metre-kilogram-second system rather than the centimetre-gram-second system.
    • The unit of pressure in the SI system is the pascal (Pa), defined as the force of one newton per square meter:
    • Since the quantities measured can have such a wide range, a standardized prefix system has been set in place.

  • Converting from One Unit to Another

    • 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.
    • There are seven SI base units, and all other SI units can be derived from these base units.
    • The seven base SI units are: [Physical Quantity: unit symbol (unit name)]
    • Derived units are based on units from the SI system of units.

  • Molality

    • The SI unit for molality is mol/kg, or moles solute per kg of solvent.
    • However, following the SI system of units, the National Institute of Standards and Technology, which is the United States' authority on measurement, considers the term "molal" and the unit symbol "m" to be obsolete, and suggests using mol/kg or another related SI unit instead.

  • Volume and Density

    • The unit for volume is a unit derived from the SI unit of length and is not a fundamental SI measurement.
    • Density is another measurement derived from SI basic units.
    • The measuring cup expresses liquid volume in the standard SI units of liters and milliliters.
    • Most American measuring cups also measure liquid in the older system of cups and ounces.

  • Covalent Crystals

    • Silicon carbide (SiC) is also known as carborundum.
    • It is found in a certain type of meteorite that is thought to originate outside of our solar system.
    • The first light-emitting diodes (LEDs) used in high-efficiency lighting were based on SiC.

  • Silicate Units, Silicate Chains, Silicate Sheets

    • The basic unit of silicate, [SiO4]4- tetrahedron, can form single and double chains and sheets.
    • The basic building block of all silicate minerals is the [SiO4]4− tetrahedron.
    • There are four covalent Si−O bonds.
    • If two [SiO4]4− tetrahedrons share an oxygen atom at one common vertex, an [Si2O7]6− ion is formed.
    • SiO4 tetrahedrons can be arranged to form sheets.

  • The Alkaline Earth Metals

    • The metals undergo transmetallation reactions to exchange ligands: $Ae+Hg{ \{ N(SiMe_{ 3 })_{ 2 }\} _{ 2 } }\rightarrow [Ae\{ { N(SiMe_{ 3 })_{ 2 }\} _{ 2 } }(THF)_{ 2 }]$ where Ae = Ca, Sr, or Ba.
    • Beryllium's low aqueous solubility means it is rarely available to biological systems.

  • The Aldol Reaction

    • By varying the metal M from Li and Na through Mg, Zn and Ti to B and Si, its influence on the diastereoselectivity of these reactions has proven to be integral, with boron providing some of the best selectivity.
    • Thus the reaction of E-enolates with aldehydes proceeds preferentially by the re (or si) face of the carbonyl reactant bonding to the same prochiral face of the enolate.
    • Conversely, similar reactions of Z-enolates occur by preferential bonding of the re (or si) face of the aldehyde to the si (or re) face of the enolate.