The speed you have to travel to escape the earth's gravitational pull is often incorrectly known as the escape velocity, true it is the speed required to escape the Earth's pull but the term velocity requires direction as well as speed, and the direction is not important in this case. If the correct speed is attained you will leave the Earth, unless your path intersects with the Earth itself, in which case your speed will rapidly decrease as you crash into it.

The actual speed required varies dependent on the point you start, close to the Earth's surface you will need a higher speed than if you are at altitude.

Gravitational pull reduces by the inverse square of the distance from the centre - this sounds complicated but really isn't such a difficult one to understand. For example if you are 1 mile from the centre of a planet the pull will be four times as much as if you were 2 miles (or kilometres, the units don't matter) from the centre. This is calculated by first squaring the numbers: 1 squared is 1 and 2 squared is 4 so we have 1 and 4, we then take the reciprocal of these 1/1 = 1 and 1/4 to find the relative gravitational pull. We find, as predicted, that the pull at 2 miles will be a quarter of the pull at 1 mile.

Given this rule we can see that the Earth's pull extends forever into space, however beyond a certain distance the pull will be so insignificant as to not matter - for instance when we leave our Solar System.

So, what speed do we need to travel to leave Earth's immediate pull?
At ground level the speed will be approximately 11.2 km/s, just over 25,000 mph or mach 34, a speed that is currently impossible to achieve.
Even at 9,000 km high the escape velocity is 7.1 km/s or nearly 16,000 mph or mach 20.

These speeds are not yet achievable by man instead the speed is built up by maintaining a force on the object, the current solution for this problem is to use rocket power.

A well-known example is the Saturn V, a three stage rocket - the first stage alone burnt over two million kilogrammes (well over two thousand tons) of fuel in two minutes and forty one seconds producing thirty four million Newtons thrust.Stages two and three require less force as the rocket is now considerably lighter, and between then accelarate the manned capsule to a speed which allows it to pull away from the Earth.