Everything in this universe is a wave as well as a particle. How much of a wave or how much of a Particle? Depends on their properties. In this dynamic universe. Plenty of sources generate sound. The sound is basically a wave which traverses through a medium. When the source generating sound moves or an object receiving that sound moves, then the magnitude of the sound he/she hears varies. Thus, there is a strong correlation between the sound wave and the motion of an object.
This was first observed and theorised by an Austrian physicist Christian Doppler during the year 1842. The revolutionary theory was named after him as the Dopler Effect. It explains the change in wavelength or frequency of the sound wave in relation to an observer who is under relative motion with the sound source.
We all have experienced Dopler effect knowingly or unknowingly. If we are standing beside a road. When an ambulance passes by, we hear the sound most. The sound gets fainter and fainter as ambulance moves farther away. In general, the Doppler effect is observed when there is a relative motion between the observer and the source.
Consider a source producing sound. When it moves, in the direction it moves the sound waves bunch up and behind it, they spread out. If the source is moving towards the stationary observer, the observer receives sound with higher frequency. More the close source move towards an observer, higher will be the sound waves observer receive. If the source is moving away from the observer, the observer will receive the waves of lower frequency. Further, the sound source move from a stationary observer, less and less will be the sound observer receive.
The Doppler effect can be observed in various scenarios. Starting from vehicles, musical instruments, animals, humans, in short anything where the sound is involved. For example: Consider the lab experiment of calculating spring constant. Where we pull a spring attached with a load and count oscillations and record necessary parameters to calculate spring constant.
In the above experiment, the moment we release the stretched spring, the spring potential energy is converted into sping kinetic energy and the damping will finally bring spring to rest. This series of oscillations will generate a sound which can be well explained through the Doppler effect.
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