Doppler Effect Demonstrator

Materials: Lazy Susan, a piece of dowel, piezo speaker, speaker wire, 9-volt battery, knife switch, duct tape.

Building Instructions: Attach the wire to the two pins on the piezo speaker. One wire should attach to the positive terminal and the other wire should attach to the switch and the switch should then attach to the negative terminal. Put speaker on a long dowel and tape everything in place on the lazy susan.

Function and Use: You are probably already familiar with the Doppler Effect. When you listen to cars or trains go by you, you hear the sound get higher in frequency (pitch) as it comes towards you and the frequency (pitch) goes down as it goes away. This is a very important concept in astronomy because it also happens to electromagnetic radiation (in most cases they use visible light). When a star or other object moves towards us its frequency goes up and it looks bluer than it should and when it moves away, its frequency goes down and it looks redder than it should (you might have heard the term "redshift" meaning objects are moving away from us).

If you put the knife switch down and spin this device fast, you should be able to hear the frequency (pitch) change as the speaker goes towards and away from you. (You may have to listen very carefully since the swing arm isn’t very long and the distance it moves towards and away from you is very small). Be careful when spinning the speaker that the speaker does not hit you! Be sure to lift the knife switch so that the battery won’t go dead.