The Doppler effect makes a pitch appear to change when you, or the source, are in motion. Now it takes longer for you to hear a certain amount of wavelengths. The opposite happens when the distance between you and a source of sound widens. If you were not moving, after 2 seconds, only 20 wavelengths would have reached you and the frequency would still sound like 10 Hertz. The frequency seemed higher because you were moving. Now the frequency you hear is 50 divided by 2, or 25 Hertz. Imagine you heard the same sound, but this time you were moving towards its source and it only took 2 seconds for 50 wavelengths to reach you. It is named for the Austrian scientist Christian Doppler (1803-1853). The frequency of that sound is 50 divided by 5, or 10 Hertz. The Doppler effect is a phenomenon observed with all waves. For example, say you heard a sound that had 50 wavelengths by the time it reached you, it would have taken it 5 seconds to reach you. If you hear a frequency in a shorter amount of time, it seems like you are hearing a higher frequency. Remember that frequency is wavelengths per time. The ball would reach you sooner if you walked towards it and later if you moved away from it. Imagine you are playing in the park and your friend rolls a ball to you. The Doppler effect happens because distance affects the amount of time it takes you to hear the sound. As the train passed by them, they heard a drop in pitch, just like Doppler predicted. To test his theory, scientists hired 15 trumpeters to play on a moving train.

If you are heading away from a source or it is going away from you, he believed the sound would seem lower than its actual pitch. What did Christian Johann Doppler discover?ĭoppler claimed that if a sound is getting closer to you, either because its source is approaching you or because you are going towards the source, the sound will seem higher than it really is.

The Doppler effect is named after the Austrian physicist, Christian Johann Doppler, who discovered it. This principle is known as the Doppler effect. The whistle is not changing pitch, but you are hearing a change. You may have noticed that a train whistle gets lower as it passes you. When we are moving, or a source producing a sound is moving, we hear things differently.

The doppler effect