The researchers tested different tea
kettles and forced air through them at different speeds.
They then plotted frequency verse amplitude until they discovered
a trend in the data. They ultimately discovered that when the
steam comes up the spout, it meets a hole when it begins to
whistle.This contracts the flow of steam as it enters the whistle
and makes a jet of steam pass through it. The jet stream is
unstable, which means that when it hits the second wall, it forms
a small pressure pulse. This pulse makes the steam form
vortices as it exits, which produces sound waves.
These sound waves are what we hear in the form of the tea kettle
whistle! The researchers also discovered that a longer spout
gives a lower tone while a shorter spout gives a higher tone to
the whistle.
Does anyone really know why a tea
kettle makes a whistling noise when the water inside of it has
reached the boiling point? Well the reason has been
unknown for quite sometime by most scientists. A tea
kettle is not the only object that makes this sort of
noise. Damaged car exhausts and plumbing with air in the
pipes make the same sort of noise. A researcher at Cambridge
university discovered that the basic tea kettle has two plates
that are generally close to each other, with holes in both of them
so that the steam can pass through them. They knew that the
sound is understood to be caused by the vibrations made by the
build-up of steam trying to escape, but they didn't know what
about the process made the sound.
