THE SI system and units of measurement

							Units of Measurement
THE SI SYSTEM AND UNITS OF MEASUREMENT
MEASUREMENT

 Measurement is used to measure quantities.
 Quantity is something that has magnitude, size,
  or amount (volume).
 In the late 18th century, scientists used the
  metric system. The metric system is a precursor
  to the SI System.
 Scientists all over the world use a single
  measurement system called Le Systeme
  International d’Units, abbreviated SI.
SI SYSTEM OF MEASUREMENT

 This system was presented in 1960 by a
  General Conference of Weights and Measures
  and has both base units and derived units.
 It is based on the metre-kilogram-second
  system and replaces both the foot-pound-
  second system and the centimetre-gram-
  second system.
 The International System of units has been
  developed and agreed internationally in the
  interests of world health.
SI SYSTEM OF MEASUREMENT
   It overcomes languages barriers, enabling an exchange of
    health information within a country and between nations to be
    made without the misunderstandings which arise when each
    country, or even a separate hospital within a country, uses its
    own units of measurements for reporting tests. It is therefore
    important for health authorities and laboratories to adopt the
    new system of units. They are not difficult and are already
    being used in most medical publications and journals, by the
    manufacturers of chemicals and reagents, and by most
    scientific and medical organizations.
   There are seven SI base units, i.e. metre, kilogram, second,
    mole, ampere, Kelvin and candela.
SI BASE UNITS

   The most common base units that we will study
    include:
                       Quantity                  Unit
          Quantity                Unit name
                       Symbol                 abbreviation

           Length         l        meter           m


            Mass          m       kilogram        kg


            Time          t        second          s


         Temperature      T        Kelvin          K
SI BASE UNITS

•   To enable the measurement of quantities larger
    or smaller than the base units or derived units,
    the SI Units system also includes a set of
    prefixes. The use of a prefix makes a unit larger
    or smaller. The ranges of SI unit prefixes are
    listed in the tables 1 and 2
TABLE 1
 Prefix   Symbol   Function       Divided by
 deci       d        10-1            10
 centi      c        10-2            100
 milli      m        10-3           1000
 micro      µ        10-6         1000000
 nano       n        10-9       1000000000
 pico       p       10-12      1000000000000
 femto      f       10-15     1000000000000000
TABLE 2
Prefix   Symbol   Function   Multiply by

deca     da       101        10

hector   h        102        100

kilo     k        103        1000

mega     M        106        1000000

Giga     G        109        1000000000

tera     T        1012       1000000000000

peta     P        1015       1000000000000000
LENGTH
 The SI standard unit for length is the meter.
 A distance of 1m is about the width of an average
  doorway.
 To express longer distances, the kilometer (km) is
  used. One kilometer is equal to 1000 m.
 To express shorter distances, the centimeter (cm)
  is used. One centimeter is equal to 1/100 of a
  meter.
 Length can be measured using a meter stick or
  rulers.
MASS
 Mass is a measure of the quantity of matter.
  The standard unit for mass is the kilogram (kg).
 The gram (g), which is 1/1000 of a kg is used
  for measuring masses of small objects. Mass is
  typically measured using a balance.
 Mass is different from weight. Weight is a
  measure of the gravitational pull on matter
  (Newton). The weight of an object increases as
  gravity acts on it.
TIME
 The standard unit of measurement for time is the
  second (s).
 Time can be measured using stop watches, clocks,
  count down timers, and other time pieces.
 Larger amounts of time are measured in minutes
  and hours.
 There are 60 seconds in one minute. There are 60
  minutes in one hour. Given that there are 24 hours
  in one day, how many seconds are there in one
  day?
TEMPERATURE
 The standard unit of measurement for
  temperature is degrees Kelvin (K).
 Temperature can also be measured in degrees
  Celsius (°C) and degrees Fahrenheit (°F).
 To convert degrees Celsius (°C) to degrees
  Fahrenheit (°F) multiply by 1.8 and then add 32.
  To convert degrees Fahrenheit to degrees Celsius,
  subtract 32 and then divide by 1.8
 ° K= °C + 273
 Temperature is measured using a thermometer.
  (measures the degree of heat or coolness)
DERIVED UNITS

   Derived units are combinations of base units.
    They are produced by multiplying or dividing
    standard units. The derived units we will study
    include:
                     Quantity                   Unit
          Quantity                  Unit
                     symbol                     abbreviation

            Area        A       square meter        m2

           Volume       V       cubic meter         m3

                                kilograms per
           Density      D                         kg/m3
                                cubic meter
AREA
 Area is length times the width. It is expressed
  as square meters.
 Area can also be expressed as cubic
  centimeters.
 What is the area of a rectangle that has an a
  length of 6 cm and a width of 16 cm?
                      16 cm




                         1           6 cm
                         11111cmam
VOLUME
 Volume is the amount of space occupied by an
  object. The derived SI unit for volume is cubic
  meters. The cubic meter is rather large, so a more
  common unit of cubic centimeters is more
  commonly used.
 Non-SI units are also used to measure volume
  such as the milliliter (mL) and the liter (L), which is
  1000 cm3. There are 1000 mL in 1 L.
 Beakers, flasks, and graduated cylinders are often
  used to determine the volume of liquids.
DENSITY

   Density is the ratio of mass to volume, or mass
    divided by volume. It can be written:
        density=mass/volume or D=m/V
    Density is a characteristic physical property of a
    substance that does not depend on the size of
    the sample. As the mass of an object
    increases, its volume increases.