Physics Notes on Gravitation and Satellite

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 program 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.

GRAVITATION (गुरुत्वाकर्षण) Full Lecture | SSC CHSL 2019-2020 | RRB NTPC 2019 | RAILWAY GROUP D