Draw a picture of a moving source and the waves surrounding it according to what you observed in this experiment. How does the spacing of the wave-fronts in front of the source compare to those behind it?
Imagine a small observer is positioned in front of cork in your picture above. As the cork approaches, the observer measures the wavelength of the waves passing by. How does this wavelength compare to that measured from behind the source?
Imagine that this same observer measures the frequency of the waves instead of wavelength. How does the frequency measured in front of the source appear to the observer compared to the frequency measured from behind?
How do these results help explain why a car's engine sounds different as the car approaches you compared with after it passes?
The Doppler Effect is present in light waves as well. As you will learn in the Color Lab, red light has a lower frequency than blue light. Based on your observations in this experiment, what can you speculate about the motion of a distant star that appears "red-shifted" to astrophysicists? (The light appears redder than expected.)