<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Hi all, sorry, i dont understand escape velocity very well, all i know that on earth, a rocket must speed up faster that escape velocity to get in to orbit. My question is, in space elevator, does the cargo need to travel at high velocity as rocket does? Imagine there is an object, maybe a building, ladder or a mountain, very high into orbit, can a person climb at a snail pace reach the mountain peak? <br />Posted by lukman</DIV></p><p>Escape velocity can be understood in terms of energy and conservation of energy. When you raise an object against the force of gravity that object gains potential energy. When you drop it that potential energy is turned into kinetic energy as it falls. Similarly if you throw an object upwards the velocity and hence kinetic energy decrease as the object nears the top of its trajectory, and then increased again as it falls. At the very top of the trajectory the object is stopped and the original kinetic energy has become potential energy.</p><p>Now gravity decreases as the square of the distance from the source. Because of that relatinship one can show, using calculus, that if the object is moved an infinite distance from the source (the Earth for instance) that the amount of potential energy is a finite number. So if you give the object an velocity that imparts a kinetic energy greater than the potential energy of an infinite displacement that object will never fall back down. That level of velocity is called the escape velocity.</p><p>In the case of an elevator or a rope climb, one is applying a force throughout the climb. So the energy is imparted at each stage in whch force is applied over a distance. Therefore you get the necessary energy from the continual application of force and not from just an initial velocity. Hence you can climb the rope slowly, or go up the elevator slowly, and still progress upward indefinitely. <br /></p> <div class="Discussion_UserSignature"> </div>