Use diagram and charts to define and explain the Doppler effect. Determine that the effect is caused by a change in the wave length as a sound approaches and leaves an observe. Discuss how the change in pitch is caused by a change in the wavelength. Using running forks and diagrams, explain how a sound wave is a series of compressions and rarefactions of air molecules. Discuss pitch change corresponding to string diameter. Indicate the maximum and minimum Hertz heard by certain animals