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Line 122: − = Projectile and Satellite Motion = − == Concept flow == − − *A projectile motion of a body thrown is due to the gravitational force. − − *Satellites are projectiles that are continuously falling in the orbit around planets − − − Let us study this picture below and analyze what happens in each of the cases. − − − [[Image:Gravitation%20for%20wiki_html_545339b5.gif]] <br> − − In the first case, the ball is just dropped from the cliff and it falls down in a straight line, subject to the force of gravity. In the second and third instances, the ball is thrown upwards, reaches a certain height and still falls down. In the third case, the ball covers a horizontal range as well. − − In all these cases, gravity is the only force acting. Without gravity, we could throw a rock upwards at an angle and it follow a straight line path. Because of gravity, however, the path curves. − − Such an object, when thrown/ projected and continues its motion on its own inertia is called a projectile. A projectile will have two components to ots velocity – the horizontal and the vertical. The horizontal component is similar to an object rolling on a plane/ along a straight line. The vertical component of the velocity is subject to the acceleration due to gravity. A projectile moves horizontally as it moves downwards or upwards. − − Imagine throwing a ball straight up. It will fall down to the same place. In this case the ball has a velocity in the vertical direction which changes with time as the force due to gravity causes an acceleration in the downward direction all the time. But suppose on were to throw a ball with only a horizontal velocity. The ball will now move with a velocity that has two components to it - one the horizontal velocity which remains unchanged as long as there is no force such as air resistance acting on it and a vertical velocity that is continually changing. This vertical velocity starts at zero - we threw the ball horizontally - and keeps increasing with an acceleration g. − − The resultant velocity is a combination of the two. This is what causes objects to follow a parabolic path when they are thrown with a combination of horizontal and vertical velocities. − The greater the horizontal component the farther the ball will travel. For short distances, and small velocities, the curvature of the Earth will make no difference. − But suppose that we throw it so hard that the horizontal distance is very large and we can no longer ignore the curvature of the Earth? − − Suppose we throw it so hard that that ball will continue to fall but will never reach the ground - the curvature of the fall of the ball is greater than the curvature of the Earth? Then the ball will become a satellite! It will move round and round the Earth - constantly falling but never reaching the ground! − − The satellite and everything in it are constantly falling towards the Earth but will never reach it. Since they are all falling with the same velocity, the satellite does not exert any force on the objects or people inside. The people inside, therefore feel weightless. remember we have a sense of weight because of the Normal force. Here the Normal force is zero and so we feel weightless. − − This is very similar to the sense of loss of weight in a lift that is accelerating downwards - except that here the acceleration is the acceleration due to gravity.<br><br>
Significance of Gravitational Force (view source)
Revision as of 10:18, 4 December 2013
, 10:18, 4 December 2013→Projectile and Satellite Motion
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== Satellite ==
== Satellite ==