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Escape Velocity
Escape velocity is the velocity, at which any object moves out of the gravitational pull of the earth. It is used in rockets, which revovle around the earth, accelerating the speed, reaching Ve, the Escape Velocity, they move out of Earth's gravity.
In 19th century, Jules Verne has written a novel 'From Earth to Moon' in which the hero Fog is inserted in a big gun, which shoots him out to the moon, but this imaginary concept was rejected as incorrect and impossilbe. But, can not a man or an object directly go out of earth's pull, if it is shot with Ev i.e. escape velocity. Or, is it necessary to move around first? Why, if so? |
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Jules Verne's concept of a giant gun is indeed plausible. No need to "move around" first as long as the projectile leaves the gun barrel at the escape velocity or greater (about 45,000 Km per hour). When a rocket is in orbit and fires its engines to escape earth gravity the speed it must attain is slightly less, because the force of earth's gravity at an altitude of, say, 200 miles is about 10% less than the earth's gravity at the earth's surface. This means the escape velocity from an altitude of 200 miles is about 3% less than at the surface. Since the rocket is in orbit and so already moving at about 28,000 KpH the incremental speed needed to reach escape velocity of 44,000 KPH is less than from the ground.
The whole concept of "escape velocity" is built around the concept that the projectile or rocket is accelerated up to that velocity and then coasts "uphill" against earth's gravity from then on. But if you have a rocket with an engine that can continuously operate there is no need to reach escape velocity at all. You can go on a leisurely trip to Mars at a stately 5 Km/hour all the way if you have an engine that will maintain that speed. Think of this analogy - in your car you can drive up a hill to the top as slowly as you want, but if you want to coast up the hill to the top with the engine off you have to start with a pretty high velocity at the bottom of the hill. |
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