Why does a ping pong ball on a string move toward a running stream of water?

Question

We keep a ping pong ball on a string near a faucet but not directly under it. When we run the water, the ball moves to the stream and sticks there.

I'm only interested in the moving part not the sticking part (there are lots of explanations for that online).

question1: Why does the ball move toward the water stream?

question 2 If we run the water and get a steady flow first, and then take the ball close to the stream, would it still move toward the water?

Answer 1

The stream of water is entraining air and dragging the air down with it. The boundary condition at the surface of the water stream is that the downward velocity of the air must match the downward velocity of the water. To make up for this entrained air, air from the surrounding region must flow radially inward toward the water stream.