How fast must a rocket travel to escape the earth?
Perhaps you hope that someday you may help to launch a space ship or put a satellite into orbit around the world. If this is your ambition, right now is the time to start. For the job calls for schooling in mathematics and it is never too early to start that challenging subject. It takes a lot of figuring to launch a rocket. Smart mathematicians work for maybe months and even then they need help from electronic brains.
It is hard work for a rocket to climb above the ground because the earth’s gravity is pulling it down. It uses its fuel to fight against gravity and rise up into space. Perhaps you have ridden on an escalator, those moving stairways they have in the big stores. If you stand still, the up escalator carries you up or the down escalator carries you down.
No doubt you have run up the escalator which is going up and got there faster, But it is a hard job to run up the escalator which is going down. A rocket has to work just as hard to launch itself because the earths gravity is trying to pull it down. The burning fuel gives the rocket a boost upward and the bigger the boost the faster the rocket is launched.
If the rocket could rise at a certain speed, it would escape the pull of the earthis gravity. This speed is called escape velocity, meaning the speed necessary to escape the gravity of our planet. Escape velocity depends upon the bulk and weight of a planet and our earth is very heavy for its size. If a rocket, a bird or baseball could reach a speed of seven miles a second, it would be free from the earth's gravity.
The earth’s escape velocity is seven miles a second, which is about 25,000 miles per hour.
A rocket, however, does not have to travel at escape velocity to leave the earth and travel to the moon. The pull of gravity gets weaker as it leaves the earth and out in space it will keep going, even without any boosting push from its fuel.
The smaller, lighter moon has less gravity than the earth. This means it has a slower escape velocity. A rocket bound, say, for Mars, could escape the moon’s gravity at about one and a half miles a second. The escape velocity from Mars is a little more than three miles a second.
Venus is about the same size as the earth, but not quite so heavy, Its escape velocity is just over six miles a second. Little Mercury, the planet nearest the sun, has an escape velocity of a little more than two miles a second. But in order to escape the pull of the giant planet Jupiter, a rocket would have to travel at 60 miles a second which is more than 200,000 miles an hour.