11_physics_8.json

{"text": "The earliest recorded model for planetary motions proposed by Ptolemy about 2000 years ago was a ‘geocentric’ model in which all celestial objects, stars, the sun and the planets, all revolved around the earth.", "fibs": ["earth"]}
{"text": "However a more elegant model in which the Sun was the centre around which the planets revolved – the ‘heliocentric’ model – was already mentioned by Aryabhatta (5th century A.D.)", "fibs": ["Sun"]}
{"text": "The law of areas can be understood as a consequence of conservation of angular momentum whch is valid for any central force .", "fibs": ["angular momentum", "central force"]}
{"text": "A central force is such that the force on the planet is along the vector joining the sun and the planet.", "fibs": ["sun", "planet"]}
{"text": "From Kepler’s second law, equal areas are swept in equal times.", "fibs": ["second"]}
{"text": "In the motion under a central force the angular momentum is always conserved.", "fibs": ["central", "angular momentum"]}
{"text": "The gravitational force of the sun on the planet is directed towards the sun.", "fibs": ["sun"]}
{"text": "Every body in the universe attracts every other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.", "fibs": ["square", "inversely", "product"]}
{"text": "The gravitational force between the spherical balls is the same as if their masses are concentrated at their centres.", "fibs": ["centres"]}
{"text": "If the position of the particle changes on account of forces acting on it, then the change in its potential energy is just the amount of work done on the body by the force.", "fibs": ["work done", "potential"]}
{"text": "The force of gravity is a conservative force and we can calculate the potential energy of a body arising out of this force, called the gravitational potential energy.", "fibs": ["conservative force"]}
{"text": "The gravitational potential due to the gravitational force of the earth is defined as the potential energy of a particle of unit mass at that point.", "fibs": ["potential", "potential energy"]}
{"text": "Earth satellites are objects which revolve around the earth.", "fibs": ["earth", "satellites"]}
{"text": "Moon is the only natural satellite of the earth with a near circular orbit with a time period of approximately 27.3 days which is also roughly equal to the rotational period of the moon about its own axis.", "fibs": ["rotational period", "earth", "satellite", "Moon", "time period"]}
{"text": "The moon is a satellite of the Earth.", "fibs": ["satellite", "moon", "Earth"]}
{"text": "If the circular orbit is in the equatorial plane of the earth, such a satellite, having the same period as the period of rotation of the earth about its own axis would appear stationery viewed from a point on earth.", "fibs": ["earth", "stationery ", "equatorial"]}
{"text": "Satellites in a circular orbits around the earth in the equatorial plane with T = 24 hours are called Geostationery Satellites.", "fibs": ["equatorial", "Geostationery"]}
{"text": "Indigenous launch vehicles were employed in the early 1980’s to send the Rohini series of satellites into space.", "fibs": ["Rohini", "satellites "]}
{"text": "In 1984 Rakesh Sharma became the first Indian astronaut.", "fibs": ["Rakesh Sharma"]}
{"text": "Weight of an object is the force with which the earth attracts it.", "fibs": ["Weight ", "force", "attracts"]}
{"text": "In a satellite around the earth, every part and parcel of the satellite has an acceleration towards the centre of the earth which is exactly the value of earth’s acceleration due to gravity at that position.", "fibs": ["acceleration due to gravity", "acceleration", "centre"]}
{"text": "The gravitational force is a conservative force, and therefore a potential energy function can be defined.", "fibs": ["potential", "conservative"]}
{"text": "The total energy is negative for any bound system, that is, one in which the orbit is closed, such as an elliptical orbit.", "fibs": ["negative", "bound"]}
{"text": "If a particle is outside a uniform spherical shell or solid sphere with a spherically symmetric internal mass distribution, the sphere attracts the particle as though the mass of the sphere or shell were concentrated at the centre of the sphere.", "fibs": ["centre"]}
{"text": "If a particle is inside a uniform spherical shell, the gravitational force on the particle is zero.", "fibs": ["gravitational force", "zero"]}
{"text": "If a particle is inside a homogeneous solid sphere, the force on the particle acts toward the centre of the sphere.", "fibs": ["centre"]}
{"text": "Angular momentum conservation leads to Kepler’s second law.", "fibs": ["Angular", "second"]}
{"text": "An astronaut experiences weightlessness in a space satellite.", "fibs": ["weightlessness"]}
{"text": "if we presume that the potential energy of the object at infinity is zero), the gravitational potential energy of an object is negative.", "fibs": ["negative"]}
{"text": "The gravitational force on a particle inside a spherical shell is zero.", "fibs": ["zero"]}