@Iluviaporos - Gravity does more than contribute to circular motion equations.
It is also the force that pulls the whole earth together just enough. If gravity was a stronger force, the universe might not be expanding the way it is, because it would have stuck together for longer after the initial Big Bang.
Kind of weird that the same circular motion might one day enable us to create gravity on space ships by setting them into a spin.
Like water stays in a bucket when you twirl it around, because it too wants to fly off in that direction, but can't because of the bucket, which itself is acting like the string in your original comparison.