An open tube end reflects sound with its energy almost entirely in air velocity

Evidence

In the second case, the wave moves from a bounded region, for example a tube, into an unbounded region, for example free space, as shown in Figure 1.24. At the boundary between the bounded and unbounded regions, the molecules in the unbounded region find it a lot easier to move than in the bounded region. The result is that, at the boundary, the sound wave has a pressure component that is close to zero and a large velocity component. Therefore, at this point, all the energy in the sound is in the kinetic energy of the moving air molecules—in other words, the velocity component. Because there is less resistance to movement in the unbounded region, the energy stored in the velocity component cannot transfer in the direction of the propagating wave due to there being less “springiness” to act on. Therefore the momentum of the molecules is transferred back to the “springs” in the bounded region, which pushed them in the first place, by stretching them still further. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 352

Categorization

• XREF: Explains why an open flute end radiates while a closed one reflects pressure — connects to how instruments like flutes and organ pipes terminate.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 352