To some, the "drip, drip" of a leaky faucet is a minor irritation; to physicists, it's a great example of the predictive powers of science. In 1996, theoretical work suggested that, as a water drop hangs from a faucet, its cone-shaped neck should always have the same internal angle at break-off: 36.2°. That was an ambitious prediction given the hugely complex dynamics of dripping water, but it was also very difficult to test with any accuracy. Now, thanks to modern technology, researchers have finally plugged all doubts. A team of engineers and physicists set up a camera that took images at up to 220,000 frames per second in front of a dripping nozzle and measured the angle of the water's neck at the moment of break-off (see close-up video of a drop breaking from its neck). The angle was 36.0°, the team reports this month in Physical Review E, within 1% of the predicted value. That confirmation is good news for inkjet manufactures, many of which would like to know how reliable computer simulations of liquid dripping are so that, for example, they can figure out the optimum height to position ink heads without resorting to costly trial and error.
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