Question

I recently noticed an interesting phenomenon while watching the tap running in my kitchen. At the time, there was bright sunlight coming in the kitchen window. As the stream was running out of the tap into the sink the sunlight was shining directly on to it.

This allowed me to observe that there were a constant appearance of water particles appearing to exit the stream for about three or four inches (approx. 10 cm) before falling into the sink. This appeared to be happening throughout the full length of the stream. What could be causing this to happen? Shouldn't the surface tension hold the stream together?

Answer 1

When water falls straight down from a faucet, it narrows due to the Bernoulli's principle, which states that as the velocity of a fluid increases, its pressure decreases. This pressure difference overcomes the surface tension forces of water, causing the stream to narrow.

Step-by-step explanation:

When water falls straight down from a faucet, it narrows because of the Bernoulli's principle. According to this principle, as the velocity of a fluid increases, its pressure decreases. So, as the water falls, its velocity increases, leading to a decrease in pressure. This creates a pressure difference between the main stream of water and the surrounding air, causing the stream to narrow.

The surface tension of water tends to minimize its surface area and hold the stream together. However, in the case of a falling stream, the pressure difference created by the Bernoulli's principle overcomes the surface tension forces, causing the stream to narrow.