Add to favorites
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