The International System of Units (abbreviated SI from the French language name Système international d'unités) is the world's most widely used system of units. The SI was developed in 1960 and, with few exceptions, is used in every country in the world.
The SI base units for the seven primary quantities are:
Quantity
Name
Symbol
Length
metre
m
Mass
kilogram
kg
Time
second
s
Electric current
ampere
A
Temperature
kelvin
K
Amount of substance
mole
mol
Luminous intensity
candela
cd
Symbols are written in lower case, except for symbols derived from the name of a person. For example, the unit of electric current is named after André-Marie Ampère, so its symbol is written "A", whereas the unit itself is written "ampere". The only exception is the litre, whose original symbol "l" is unsuitably similar to the numeral "1"; thus it is recommended that "L" be used instead.
Abbreviated symbols should not be pluralized: for example "25 kg", not "25 kgs".
Symbols do not have an appended period (.) unless at the end of a sentence.
A prefix may be added to units to produce a multiple of the original unit. All multiples are integer powers of ten. For example, kilo- denotes a multiple of a thousand and milli- denotes a multiple of a thousandth. The SI main prefixes are as follows:
Name
giga
mega
kilo
hecto
deca
deci
centi
milli
micro
nano
Symbol
G
M
k
h
da
d
c
m
µ
n
Factor
109
106
103
102
101
10-1
10-2
10-3
10-6
10-9
Quantities
Quantities are the measurable properties of the physical bodies. Some of the most important ones are the following:
Mass
Is the amount of matter in a body. Its unit in the SI is the kg.
Volume
Tells how much space an object occupies. Its unit in the SI is the m3.
Capacity
Is the amount of space that can be contained by a body. It is measured in L.
Density
Expresses how concentrated is the matter in a body, this is, how much matter is there in a given unit of volume in a body. It is always the same for the same type of substance, this is, it doesn't depend on the size of the object. Its unit in the SI is the kg/m3.
Temperature
It is not a kind of energy but a measure of the amount of heat in a body. It depends on the movement of its particles: the quicker the movement, the higher the temperature. Its unit in the SI is the K, but is commonly expressed in °C or °F.
Characteristics of Some of the Common Chemical Elements Found in the Earth's Crust
KEWL - Materials and their properties.A good overall introduction to the states of matter, the atoms, the Periodic Table, elements, compounds, mixtures, separation of mixtures, and more basic chemistry topics.
Measuring devices.Measuring devices of temperature, time, weight, thickness, distance, length and angles in the Visual Dictionary.
Units of measurement.Learn the most widely used units (and its abbreviations and equivalences) for area, length, load, mass, speed, time and volume.
Atoms and Molecules
Chemistry.Images, definitions and pronunciation of matter components, chemical elements and laboratory equipment in the Visual Dictionary.
Structures and bonding.To know that elements combine through chemical reactions to form compounds and that compounds contain different elements that are chemically bonded together. Interactive lesson at Skoool.co.uk.
Periodic Table of the elements (2).Another Periodic Table with good information about the structure of every chemical element, its name, its discovery and its utility.
Periodic Table of the elements (3).In many different languages and with links to the Wkipedia articles on each one of the chemical elements.
Build an atom.Build interactively your favourite atom. (You've got one, don't you?). Tip: hit the "Next" button to the bottom, scroll up, and then hit "Enter" in your keyboard consecutively to not no have to scroll vertically anymore.
Uses of some elements.Understand how the properties of some elements relate to how they are used. Interactive lesson at Skoool.co.uk.
The particle theory.Learn how to use the Particle Theory to explain the properties of solids, liquids and gases. Interactive lesson at Skoool.co.uk.
Change of state: water.Understand what happens when a substance changes state. Interactive lesson at Skoool.co.uk.
Melting and boiling point.Understand what happens, in terms of energy and particle movement, when a substance changes state. Interactive lesson at Skoool.co.uk.
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ContactRecommendAboutU.R.L.: http://www.sciencehelpdesk.com/unit/science1/2Last updated: 06 May 2008Printed: 13 May 2008
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Science Helpdesk is a website meant to help on developing the scientific contents for the Bilingual Project Integrated Curriculum designed by the Spanish Ministerio de Educación y Ciencia and the British Council.
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