Current Affairs For India & Rajasthan | Notes for Govt Job Exams

Science

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WORK
Work is said to be done, if force acting on a body is able
to actually move it through some distance in the direction
of the force. Its SI unit is a joule.
ENERGY

  • Energy is a scalar quantity and its unit is Joule.
  • The sum of all kinds of energies in an isolated system
    remains constant at all times. This is the law of
    conservation of energy.
    POWER
    Its unit is watt.
  • 1 watt hour = 3600 Joule
  • 1 kilowatt hour = 3.6 x 106 joule
  • 1HP = 746 watt
    GRAVITATION
  • Everybody in the universe attracts other body by a
    force called force of gravitation.
  • The gravitational force of the earth is called gravity.
  • The acceleration produced in a body due to force of
    gravity is called acceleration due to gravity (g) and
    its value is 9.8 m/s’
  • Acceleration due to gravity is independent of shape,
    size and mass of the body.
  • Escape velocity is the minimum velocity with, which
    an object just crosses the Earth’s gravitational field
    and never returns. Escape velocity at the Earth’s
    surface is 11.2 km/s.
  • Escape velocity at the Moon’s surface is 2.4 km/s.
    Due to low escape velocity there is no atmosphere on
    the moon.
  • Value of g decreases with height or depth from Earth
    surface.
  • g is maximum at poles.
  • g is minimum at equator.
  • g decreases due to rotation of Earth.
  • g decreases if angular speed of Earth increases and
    increases if angular speed of Earth decreases.
  • The acceleration due to gravity at the moon is one-
    sixth that of the Earth. So, the weight of a person on
    the surface of the moon will be 1/6 of his actual
    weight on the Earth.

SATELLITE

  • Satellites are natural or artificial bodies revolving
    around a planet under its gravitational force of
    attraction.
  • Moon is a natural satellite, while INSAT-B is an
    artificial satellite of Earth.
  • The period of revolution of satellite revolving near the
    surface of earth is 1 hour 24 minutes (34 minutes).
  • Geo-stationary satellite revolves around the Earth at
    a height 36000 km (approx).
  • Time period of rotation of geo-stationary satellite is 24
    hours.
  • The Earth rotates on its axis from West to East. This
    rotation makes the Sun and the stars appear to be
    moving across the sky from East to West.
  • A geosynchronous satellite is a satellite in
    geosynchronous orbit, with an orbital period the same
    as the Earth’s rotation period.
  • A special case of geosynchronous satellite is the
    geostationary satellite, which has a geostationary
    orbit – a circular geosynchronous orbit directly above
    the Earth’s equator.
  • Geo-stationary satellite is used to telecast. TV
    programmes from one part of the world to another, in
    weather forecasting, in predictions of floods and
    droughts.
  • Polar Satellite Revolves around the earth in polar orbit
    at a height of 800km (app.) Time periods of these
    satellites is 84 min

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