The following question came up in a swimming pool:
The pool has a jet that releases water below the surface. When I put my right hand in the water, several feet away from the jet, I can feel the pressure from the jet. (I believe that technically, I'm feeling a longitudinal wave created by the jet - is that so?) If I then put my left hand directly in front of the jet, it deflects the wave and I no longer feel the pressure on my right hand. When I remove my left hand, I once again feel the pressure.
When I remove my left hand from blocking the jet, it takes a second or so before I once again feel the pressure. This makes sense - it takes time for the wave to travel through the pool. However, when I block the jet, I stop feeling the pressure on my right hand immediately. Why is this so? I would have guessed that analogous to the unblocking case, the wave already past my left hand would continue to travel for another second, so I wouldn't immediately stop feeling it.
Please help me so that I can swim peacefully once again!