frequency shift

Frequency shift occurs when the wavelength or rate of a wave changes due to relative motion between the source and the observer. When the source moves toward you, the waves compress, increasing the frequency—this is called a blueshift. When it moves away, the waves stretch out, decreasing the frequency—known as a redshift. This principle is observed in sound (like sirens) and light (such as stars moving in space). Essentially, it’s a way to measure how objects move relative to each other based on changes in wave patterns.