In the latest video from YouTubers The Slow Mo Guys, curious camera operator and host Gavin Free used a defenceless apple and a 150psi air compressor to demonstrate the Coandă effect. This is when a moving fluid which comes in contact with a convex surface follows its curve, rather than continuing on its initial path.
“As the jet of air bounces off one side of the apple, it creates an area of low pressure between the air and the curved surface,” explained Free. “This area of low pressure effectively pulls in the airflow, allowing it to follow the curve of the apple. At this point, as the curved surface of the apple is putting a force on the air, the air exerts an equal and opposite force upward on the apple.”
This effect caused the apple to levitate above the jet of air, rapidly spinning and increasing in speed until it finally tore apart. In fact, the apple spun too quickly for Free’s trusty Phantom camera to catch even at 1,000 FPS, prompting him to borrow an even slower motion camera from Smarter Every Day’s Destin Sandlin to film it at 28,500 FPS.
“One full rotation in 9.1 milliseconds, that’s 109 rotations per second,” Free noted after some quick calculation. “Which reveals the apple’s ‘nope speed’ to be 6,565 RPM.”