SI System                                                Some Practical Units of Length
                   BASIC UNITS                               1 light-year (ly) = 9.46 × 1015 m
                                  Unit                       1 AU or ua = 1.5 × 1011 m
Dimension              Unit                 Symbol
Length                 meter         m           l           1 parsec = 3.084 x 1016 m ≈ 3.26 ly
Mass                   kilogram     kg          m            1 nautical mile = 1.85200 km
Time                   second        s           t           1 micrometer or micron = 1×10−6 m
Electric Current       ampere        A           I
Temperature            kelvin        K          T
                                                             1 angstrom (Å) = 10−10 m
Luminous               candela      cd          J
Amount of              mole         mol         N
angle                  radian      m·m−1       rad
solid angle            steradian m2·m−2         sr
Important Derived Units                                  Some Practical Units of Mass
Derived                                                      1 quintal = 102 kg
             Definition                SI Unit
quantity                                                     1 metric ton = 103 kg
Area         Length square             m2                    1 atomic mass unit (amu) or dalton = 1.66
Speed /      Displacement per unit                            x 10-27 kg
Velocity     time                                            1 pound = 0.453592 kg
Force        Mass x Acceleration       Kgms-2
                                                             1 Chandrasekhar limit = 1.44 mass of the
                                                              sun = 2.864 × 1030 kg
    Motion is a change in position of an object         Kinematics
     with respect to time.
                                                         It is a branch of mechanics, which deals with
    It is typically described in terms of               the motion of object.
     displacement, direction, velocity,
                                                         Distance (S)
     acceleration, and time.
                                                             It is the length of actual path followed by
Scalar quantity                                               an object in a particular time interval
                                                              during a motion.
It is a physical quantity which has only                     It is a scalar quantity and its unit is meter.
magnitude. e.g., mass, length, time, work, etc.
                                                             Its dimensional formula is [M0L1T0].
Vector quantity                                          Displacement ( S )
It is a physical quantity which has magnitude                It is a vector that is the shortest distance
as well as direction. e.g., velocity,                         from the initial to the final position of an
displacement, acceleration, etc.                              object during a time interval.
                                                             It is a vector quantity and its unit is meter.