When we kept the Earth's mass the same, but shrank its size, we saw that had an effect on its escape speed. Albert Einstein used
to perform what he called "thought experiments". Let's do a thought experiment in which the Earth's mass stays the same, but we keep packing that mass into a smaller and smaller size. Would we ever get to a point where there is no possible way for a spacecraft to escape the Earth? If so, why? (Hint: There's an important fact in Chapter 1 which is relevant to answering this question correctly.)
The escape velocity is the velocity needed by any object to overcome the gravitational force of the planet on which it’s present. Now we know that the gravitational force is directly proportional to the mass of the planet and inversely proportional to the distance of the object from the center of planet.
If we keep the mass of earth constant and decrease the size of the earth than this will decrease the distance between the object and the center of the earth and thus the gravitational force that will act on the body will increase substantially which will in turn increase the value of the escape velocity.
The value of escape velocity will keep on increasing as the size of the earth will shrink till it reaches to a point when the value of escape velocity becomes more than the speed of light and since it’s impossible to travel with a speed greater than the speed of light and therefore at this point it will become impossible for a spacecraft to escape the earth.
