WHY SATELLITES NEVER FALL BACK TO THE PLANET OR TO SPACE

 WHAT IS A SATELLITE ?

    A satellite is a body which continuously revolves around a much larger body in stable orbit. Satellites are of two types:- Natural Satellite and Artificial Satellite. Natural satellite is the one which is not man made. For example, Moon is a natural satellite of Earth and even all the planets revolving around sun act as a satellite of sun . Artificial satellite is a man made satellite. For example the robotic satellites that revolves around the planet for communication and space research are artificial satellites.

ARTIFICIAL SATELLITE

NATURAL SATELLITE

WHY DO WE NEED SATELLITES ?

      Satellites find many applications in our life. They help in sending television signals directly to homes and also act as backbone of network TV and cable. They are also used in navigation. They also provide in-flight phone communications on airplanes. They provide the primary timing source for cell phones and pages. Satellites also provide meteorologists with the ability to see weather on a global scale.

SATELLITE NAVIGATION

SATELLITE  FOR TELEVISION AND COMMUNICATION

SATELLITE FOR INFLIGHT COMMUNICATION

 

HOW SATELLITES ARE MAINTAINED IN THE ORBIT OF THE EARTH ?

       According to the theory of gravitation given by Sir Isaac Newton, every object in the universe attracts other objects with a force which is directly proportional to the product of the masses of two bodies and inversely proportional to the square of the distance between them. This force is called force of gravitation. If one of the object is earth then, that force will be called force of gravity.

   If an object is thrown upwards by using any suitable force, then that object would travel up to a height where it's velocity becomes zero and would return back to the ground. This is because Earth attracts the object towards it by the force of gravity due to its large mass.

GRAVITATIONAL FORCE

EARTH'S GRAVITATIONAL FIELD

    This would lead us to a fact that, for an object to escape out of the Earth, it would require a large velocity so as to overcome the gravitational force of attraction of Earth. This velocity is called escape velocity. For Earth, escape velocity is about 11.2 km/sec. It varies from planet to planet.

      If an object is thrown with a velocity equal to the escape velocity of earth, then it would be able to escape earth's gravitational field but after escaping from earth, it would soon come to rest whereas, if it is given a velocity more than the escape velocity then after escaping from Earth, it would continue to move in space till it comes under the influence of the gravitational pull of some other planet.

     The satellites surrounding the Earth are launched in the same way they are given the velocity to escape the earth and they come to rest when they reaches the orbit of Earth. In the circular orbit they experience the centripetal force of the Earth which is directed towards the centre of the Earth. In order to maintain itself in the circular orbit of Earth, it moves with an orbital velocity which is equal to 7.9 km/sec. In this way it neutralizes the centripetal force and maintains itself in the circular orbit.  

SATELLITE ORBITING AROUND THE EARTH

ORBITAL VELOCITY