How tall is this building?

Sorry but I don't like the centrifugal force notion. There is only one force acting in the system and that is gravity. The penny is simultaneously moving laterally with constant velocity, and accelerating down towards the Earth. It never gets closer to the Earth though because its lateral motion ensures that the curving of the Earth's surface away from it, exactly matches the distance through which it falls. This is a hard thing to put into words and others have done it better. Sketches help too.

There's talk on here of centripetal forces, but that doesn't help really since they only have meaning with circular motion, and as we know orbits under gravity can be elliptical or even hyperbolic. So I think notions of circularity in these discussions don't help. Cometary orbits for instance can be highly elliptical, so much so that when they are far out in the solar system such comets may actually look as though they are falling towards the sun. The key word is "falling". This is really what the penny is doing even though its motion is actually circular.

This is interesting now. One guy below was talking about centrifuges. Imagine you're standing in a cradle that some giant is swinging around on a rope. Just like standing on the Earth you feel a floor beneath your feet and it feels like there's a force pulling you "down" (or outwards if you prefer) to that floor. This is why the notion of centrifugal force is so popular - because we've all experienced it. So why in the ISS aren't the astronauts thrown against the further wall of their space station? In both cases there is only one force acting, the rope wielded by the giant, or gravity in the ISS. And yet the astronauts drift weightlessly whilst you in your cradle are anything but. The difference between these two situations is as follows. The centripetal force applied to you by the rope is applied via the cradle floor. As you go up through your body, slice by slice, each slice applies and reacts the forces to the slices above and below, just like standing on the Earth. So it's like a pile of books on a table. The uppermost book only feels itself whereas the lowermost has to carry the force of all of them to the table. On the ISS however, the force of gravity isn't applied to an astronaut locally, through a floor or wall. It is applied to each and every atom and elementary particle of his body simultaneously.. So there is no stacking, slice upon slice. Every slice experiences the exact same force as every other. It's as though, instead of a single solitary rope, gravity has a vast number of ropes all pulling with the same acceleration on every particle of the astronaut's body, simultaneously.