Sound Sound is a mechanical wave that is alternating bands of high pressure and low pressure longitudinal wave requires a medium travels fastest though solids, slowest through gasses Pitch – variations in sound frequency

Doppler Effect

The Doppler effect (Doppler shift), named after Austrian physicist Christian Doppler who proposed it in 1842, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches and passes an observer. The apparent frequency is higher (compared to the emitted frequency) during the approach and it is lower as the object moves away.

Object at rest

Object moving

Object moving at the speed of the waves it is producing (water, sound, light…)

The Doppler Effect

Practical Applications of the Doppler Effect Astronomy - for electromagnetic waves such as light results in either a so-called red shift or blue shift. It has been used to measure the speed at which stars and galaxies are approaching or receding from us

Practical Applications of the Doppler Effect Law enforcement - to measure the velocity of detected objects. A radar beam is fired at a moving target — e.g. a motor car, as police use radar to detect speeding motorists — as it approaches or recedes from the radar source Medicine - An echocardiogram can produce accurate assessment of the direction of blood flow and the velocity of blood and cardiac tissue using the Doppler effect. These measurements allow assessment of cardiac valve areas and function, any abnormal communications between the left and right side of the heart, any leaking of blood through the valves, and calculation of the cardiac output.

Practical Applications of the Doppler Effect Meteorologists use a similar principle to read weather events. In this case, the stationary transmitter is located in a weather station and the moving object being studied is a storm system If the clouds or precipitation are moving away from the station, the frequency of the waves reflected back decreases. If the clouds or precipitation are moving toward the station, the frequency of the waves reflected back increases. Computers in the radar electronically convert Doppler shift data about the reflected radio waves into pictures showing wind speeds and direction.

Practical Applications of the Doppler Effect Echolocation, also called biosonar, is the biological sonar used by several animals such as shrews, most bats, and most cetaceans (whales, dolphins, and porpoises).

Questions? 18