Two players hit a tennis ball over the net indoors and then move outside and do the same thing on an court with exactly the same surface as the indoor court. It is a very calm day with no wind at all. The players don't change anything in their hitting.
In theory the ball should fly with exactly the same speed and trajectory outdoors as indoors. In practise though, the game is always slower outdoors. Can this be attributed to the fact that there is always at least a very small wind (air moving)outside, or is there some other explanation to this?