Speed

Shea says this:

Sound travels 1130 ft/second in air at room temperature
Much slower than the speed of light, as we all know
Hammer a nail or hit a golf ball at a distance, we see and hear that the sound comes later
That is, reality is out of sync!
Filmmakers force into sync sounds that in reality would be late.
Generally, film and television sound should be in hard sync with the picture, despite the effects of the speed of sound
Speed of sound dependent on the medium: faster in denser media
Faster in water than in air
Faster in steel than in air (that's why we listen to the steel rail to hear when the train is coming)
What happens in a large theatre during the time it takes for sound to reach the audience?
Most of us can easily see when film is two frames out of sync
Pull up the sound by one frame in motion picture release prints, so the sound comes early
In a large theatre the film will be out of sync for some, in sync for others