Final answer:
The Doppler effect is used to measure an object's speed by observing the shift in frequency or wavelength of waves, such as light or sound, as the object moves towards or away from an observer.
Step-by-step explanation:
The Doppler effect is used to measure the speed of an object by observing changes in the frequency or wavelength of waves emitted or reflected by the object as it moves toward or away from an observer. The principle behind this is that when an object is moving towards the observer, the waves are compressed, leading to a higher observed frequency (or a shorter wavelength), which is known as a blue shift. Conversely, when the object is moving away, the waves are stretched, resulting in a lower observed frequency (or a longer wavelength), known as a red shift.
For example, in astronomy, we can measure the radial velocity of a star by comparing the known laboratory wavelength of light (emission or absorption lines) to the observed wavelength which is Doppler shifted due to the star's motion. The difference in wavelength allows us to calculate the star's velocity using the known speed of light. Similarly, Doppler-shifted radar is used to measure the speed of cars, the velocity of blood in medical ultrasound, and the velocity and direction of storm motion in meteorology.