```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
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
Intensity
Amount of              mole         mol         N
Substance
SUPPLEMENTARY UNITS
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
m/s
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
Motion
    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.
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