Sorry, random post here. This breaks my mind. My son saw on his home security cam that the AC compressor blades were turning oh so slowly. 

He went outside to investigate.

Sure looks slow—to the human eye. Both his sec cam and iPhone (!) shutter speeds were nearly as fast as the rotor blades, giving the illusion of slow movement. I was in disbelief. He sent me this additional video:

 😳

So what's "real"?