The building is contiguously attached to the ground (unless it's some sort of flying building). You need to be more than two metres away from it and falling to count as 'falling from the sky'.

For safety reasons, it's probably also better to throw an object - I'd suggest a tennis ball - if you actually want to perform an experiment. You could get it to the state 'falling from the sky' by throwing it hard enough horizontally from a fourth- or fifth-floor window, or dropping it off a bridge.

Hmmm... I may need to update my definition to consider the 'dropped-from-a-bridge' case.