## Due 3:30 pm, Thursday, December 10th

Physics 105, Fall Term, 2009

Did you complete the reading assignment?

Yes
No

## KEY CONCEPTS:

1) The Doppler Effect is an observed shift in frequency caused by the motion of the observer or source.

2) The actual frequency of the sound is not shifted, just the frequency that the observer notices seems different.

The Doppler Effect is a topic that everyone has experienced in their lives. Whether it is the change in pitch of an ambulance siren as it passes you on the road or the changing pitch of racecars going past the cameras when you turn on ESPN looking for sports and get stuck with NASCAR. The Doppler Effect really happens with all waves, but we are only able to recognize it in daily life with sound waves. Go to: http://www.colorado.edu/physics/2000/applets/doppler.html to see a physical representation of the sound waves relationship to an observer when a source of sound is moving.

Increase the speed of the police car by moving the scroll bar all the way to the right. To an observer that the cop car is traveling toward, how do the wavelengths compare to when the car is not moving?

The wavelengths are closer together
The wavelengths are farther apart
The wavelengths are the same

To an observer that the cop car is traveling away from, how do the wavelengths compare to when the car is not moving?

The wavelengths are closer together
The wavelengths are farther apart
The wavelengths are the same

How would the pitch of a siren sound to you (compared to the actual pitch of the siren) when a police car is moving toward you?

The pitch would sound higher
The pitch would sound lower
The pitch would sound the same

How would the pitch of a siren sound to you (compared to the actual pitch of the siren) when you are sitting in a police car?

The pitch would sound higher
The pitch would sound lower
The pitch would sound the same

A police radar gun is an application of the Doppler Effect. It works by sending out an electromagnetic wave of a specific frequency at a car and measuring the frequency of the wave as it reflects off the car. It then takes the difference between the emitted frequency wave and returned frequency wave to calculate your speed. Why must the the police measure your speed while you are headed directly toward the gun?

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Was there anything that you didn't understand in the reading assignment?  What was confusing to you?