Faster airflow through a constriction reduces pressure against the walls

Evidence

As air flows past a constriction, in this case the lips, its velocity increases. The Bernoulli effect is based on the fact that at all points the sum of the energy of motion, or “kinetic” energy, plus the pressure energy, or “potential” energy, must be constant at all points along the tube. Figure 4.25 illustrates this effect in a tube with a flexible constriction. Airflow direction is represented by the lines with arrows, and the velocity of airflow is represented by the distance between these lines. Since airflow increases as it flows through the constriction, the kinetic energy increases. In order to satisfy the Bernoulli principle that the total energy remains constant, the potential energy or the pressure at the point of constriction must therefore reduce. This means that the force on the tube walls is lower at the point of constriction. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1264

Categorization

• DEFINE: Clear explanation of the Bernoulli principle as it applies to brass embouchure, grounding the reed vibration mechanism.
• CANDY: The counterintuitive fact that faster airflow lowers local pressure is a memorable elevator-science tidbit.