- Education and Science
Rockets don't attain 'Escape Velocity' to get out of gravitation.
Definition of 'Escape Velocity'
Gravitation of any planet or star attract nearby objects towards it, when objects lying on the surface lifts off or jump with some force also fallback to the surface because of gravitational attraction. Now if the jump or the lift off is so powerful that the object doesn’t fell back then the initial velocity of the object is said to be more than escape velocity. Minimum initial velocity of object required when it shoot up to escape the gravitational attraction is called escape velocity.
Most of the people believe...
Above definition is misunderstood that rockets and space shuttles which overcome the attraction of gravitation of earth and moon need to attain this escape velocity to get out into the space. Even some teachers and professors in school teach their students that the speed of rockets can reach 11 Km/s which is the minimum initial velocity required to get out from the planet earth. On the contrary the fact is that the helium or hydrogen filled balloons can also reach to edge of the atmosphere with the speed much less than escape velocity. So the reality is that any object which has continuous upward thrust can escape the gravitation, only it needs to overcome the downward acceleration produced by gravitational pull (the downward acceleration on earth near the surface is 9 m/s).
Now you can also ask, why the helium balloon stops on the edge of atmosphere? The answer is because until now it was pushed upward by the heavier air around the balloon but at this altitude air was absent to push helium further. In the same manner engines of airplanes and helicopters need air around them to produce thrust, so they are unable to work when air gets thinner at higher altitudes. And the mechanism of rocket engine is able to work without air around it, so it is able to escape into space without falling back.