Forces in 2-D and Circular Motion

The Big Questions:

1. How do forces cause objects to move in circles?

In order for objects to move in circles, there needs to be a force towards the center of the circle. In our lab, we turned on the hover discs therefore extracting the force of friction. Attached to the hover disc was a string that was being held onto by a person. Acting as the center of the circle/orbit, the person exerted a force on the string and by pulling it towards them, caused the hover disc to circulate perfectly. This a real small picture example with such a HUGE picture idea; it explains how the earth orbits! 

2. What does it mean to be in orbit? How do satellites orbit planets and how do planets orbit the sun?

Just like the hover discs orbited around the person, satellites orbit around the earth and the earth orbits around the sun. Both contain the idea that there is a force toward the center of the objects orbital path keeping everything on course. For satellites, because of the speed the station is traveling at, they are actually in constant free fall. But then why don't they just fall back to earth? Due to the Earths roundness, the space station seems to be orbiting the Earth when it is truly falling but being pulled towards the earths core.