It starts with a low pitch that increases with time; highest when nearest to you, and lowest as it moves away from you.
Its always fun listening to the sound of cars as they pass by especially while hooting, but have you ever thought about the science behind it?
The doppler effect, occurs when there is relative change of frequency of a wave in relation to the observer who is moving relative to the source.
Sounds complicated? Well it just means that if either the source of the sound, or the person listening to the sound is moving, then the frequency, or pitch of the sound will seem to change. This occurs only as long as the relative velocity is less than the speed of sound in that medium. Faster than that and voila! You get a sonic boom. But that is a story for another day.
As the source of the sound approaches you, the waves bunch up together, hence seeming to have a smaller wavelength, and higher frequency. But as It moves away from you, the distance between the waves increases hence a lowering of the pitch.
For those wondering where you are going to use this information, repeat this statement at social events to sound smart.
The discovery and Function
The doppler effect, discovered by Christian Doppler in 1842, has been used in many fields; from radar, echocardiograms, to measuring how fast the universe is expanding. We may take a look at some of these scenarios.
Radar stations are used to detect the presence of an aircraft in airspace, be it civilian or military. By measuring the doppler effect of the detected waves, one is able to measure the speed at which the aircraft is approaching, and in what direction it is coming from. It may also be used by police to detect how fast a car is moving. Now you know why it is almost impossible to get away with over-speeding
The Doppler and the Universe?
Ever wondered how scientists can tell whether the universe is expanding or contracting? Or whether its size remains constant? Well, if they cannot use a ruler or travel to space to assert such claims, how then do they know this?
Scientists use the concept of redshift; a case of the doppler effect, except this is only operational for light waves. By observing the colours of the stars over a period of time, that is, the wavelength of their emitted light, and comparing it over time, scientists are able to tell whether stars are moving towards or away from us, or our star to be particular.
Stars that move towards us bring about a blueshift (due to the fact that the color blue has a smaller wavelength hence a higher frequency) and those that move away from us show a redshift (red being the visible colour with the largest wavelength hence lower frequency).
A popular reference to the doppler effect includes Sheldon’s outfit to a Halloween party where he dressed as the doppler effect and tried giving everyone clues to what he represented. (Peep Season 1, Episode 6)
Now you Know.
For this and more, join us every week. Feel free to ask questions about everyday phenomena, and how they work. That’s all folks.
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