Newton's Law of Universal
Gravitation: Every particle of matter in the universe attracts every other
particle with a force which is directly proportional to the product of their
masses and is inversely proportional to the square of the distance between
Gravitational Field: The space surrounding any mass is
called a gravitational field.
Gravitational Intensity: The gravitational
intensity at any point in a gravitational field is defined as the force
acting on a unit mass placed at that point.
Gravitational Potential Energy: The gravitational
potential energy at a point in the gravitational field is defined as the
amount of work done in bringing the body from infinity to that point.
Gravitational Potential: The gravitational
potential at any point in a gravitational field is defined as the work done
to bring a unit mass from infinity to that point.
Orbital Velocity (Critical Velocity or Proper Velocity):
horizontal velocity with which a satellite must be
projected from a point above the earth's surface, so that it orbits in a
circular path around the earth, is called the orbital velocity or critical
velocity of the satellite.
Escape Velocity: The minimum velocity with which a body
should be projected from the surface of the earth so that it escapes the
gravitational field of the earth is called the escape velocity of the body.
Period: The time taken by the satellite to complete
one full revolution around the earth is called period or time period.
Binding Energy: The minimum energy which must be supplied
to a body, so that it can escape from the earth's gravitational field, is
called the binding energy.
Satellite: Any smaller body, which revolves around a
larger body under the influence of gravitation, is called a satellite.
Natural Satellite: A heavenly body revolving around its
planet in a stable orbit is called a natural satellite.
Earth Satellite: An artificial satellite put in its orbit
around the earth is called an earth satellite.
Geostationary Satellite (Communication or Stationary or
Synchronous Satellite): A satellite, which appears to be stationary when it
revolves around the earth from east to west in an orbit coplanar with the
equatorial plane at a height of about 36,000 km above the surface of the
earth is called a geostationary satellite. Such an orbit is called a geostationary
or synchronous or parking orbit. Its period is 24 hours.
Weightlessness: Weightlessness is the state when the
apparent weight experienced by a body becomes zero. The term "Zero
gravity" is also used to describe the state of weightlessness.