Ok, so the story goes, I was out running and I came across an old abandoned well.
Fascinated, I attempted to spit in it, to determine how deep it was.
I counted the seconds, and then tried to remember the equations for a falling body. It is distance equals one half of the gravitational constant (because I was on earth at the time, near the surface; which I recommend, you really should try it) times time distance squared.
So that nets you meters, but then you have to convert to ft because I don't think in meters, and I couldn't remember if you divided or multiplied by three point three...
Anyhow, this app does all the math for you.
Just spit or drop a rock or piece of dirt, count the number of seconds until it hits the bottom and enter into app.
Just, please, do not drop any object on any other object that might care. No people, cars, etc.
I will not be held responsible if you do.