Jets are ubiquitous in our lives. Behind the scenes, they appear in aircraft engines and rockets, and also in many industrial processes. Jets are also known to produce very sharp and loud whistle-like tones under the right conditions. These strong acoustic waves can be damaging not only nearby people's hearing, but also to structures surrounding the jet.
Here we observe a special configuration, the impinging jet, which is particularly loud. The axial mode is shown in slow-motion, photographed in HD at 20,000 fps with a state-of-the-art camera and phase-locked to the ultrasonic impingement tone, 80kHz. The mesmerizing back-and-forth dance of the jet reveals why the jet produces such loud tones. The scale of the experiment also allows the acoustic waves themselves to be observed, unveiling the feedback loop mechanism.