So far, we have only considered stationary sources of sound and stationary listeners (or observers). However, if either the source or the observer is moving, things change. This is called the Doppler effect. Like the idea of feedback, covered in the last two sections, the Doppler effect has many important applications. Because the Doppler effect depends on things moving, it can generally be used to determine the motion or speed of an object. Objects of interest may be the speed of a car on the highway, the motion of blood flowing through an artery, the rotation of a galaxy, even the expansion of the Universe.
Bodies in space that are moving away from us give off long wavelengths of light that look red, Those moving toward us give off shorter wavelengths that appear blue.
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the elements/substances do not get attracted by a magnet are called non - magnetic substances. examples : wood, cotton, plastic et cetera.
the three elements have strong magnetic properties are :
these substances are easily attracted by a magnet.