"I love hearing that lonesome wail of the train whistle as the magnitude of the frequency of the wave changes due to the Doppler effect."

http://en.wikipedia.org/wiki/Doppler_radar A Doppler radar is a specialized radar that makes use of the Doppler effect to produce velocity data about objects at a distance. It does this by beaming a microwave signal towards a desired target and listening for its reflection, then analyzing how the frequency of the returned signal has been altered by the object's motion.

The Doppler Effect- the change in wave frequency resulting from motion of the source or observer Consider the waves from a sound source: Now, consider the waves from a moving source: You hear a lower frequency as it moves away from you You hear a higher frequency as it moves toward you

A source of sound is moving toward you at a speed much less than the speed of sound. Which of the following is NOT true? the frequency of the waves behind the source is lower than the source frequency the wavelength of the waves in front of the source is shorter than the source’s wavelength (when stationary) the speed of the waves in front of the source is faster than the speed of waves behind the source. the frequency of the waves you hear is higher than the source frequency

A) It is traveling faster than truck Y. Multiple Correct: Two fire trucks have sirens that emit waves of the same frequency. As the fire trucks approach a person, the person hears a higher frequency from truck X than from truck Y. Which of the following statements about truck X can be correctly inferred from this information? Select two answers. A) It is traveling faster than truck Y. B) It is closer to the person than truck Y. C) It is speeding up, and truck Y is slowing down. D) Its wavefronts are closer together than truck Y. Based on the Doppler effect, only speed matters. The faster a vehicle is moving, the closer together the sound waves get compressed and the higher the frequency. Take the case of a very fast vehicle traveling at the speed of sound; the compressions are all right on top of each other. So faster speed means closer compressions and higher frequencies.

Doppler Effect Which water spider is moving the fastest along surface of the water based upon the water-wave pattern it is creating? A. B. C. D. All the same E. Can’t be determined

Doppler Effect What is heard if the source of a sound wave is coming towards you according to the Doppler effect? It gets louder It is a higher pitch Both of these None of these

Doppler Effect Which object is the Doppler Effect going to be demonstrated in a more drastic way (greater change in frequency)? An object emitting a louder sound An object moving faster An object emitting a higher pitch sound All of these

NOT required in AP Physics1 Doppler or apparent frequency Velocity of wave medium NOT required in AP Physics1 Velocity of Sound source Sound source frequency Which to use + or - ? Use + if sound source is moving away (Away ~ Add ~ +) Use ─ if sound source is approaching

Doppler Shift Examples Red/Blue Shift: Police Radar:

Web link: The Doppler Effect and Sonic Booms Stationary Sound Source Source moving with vsource < vsound Source moving with vsource = vsound (Mach 1 - breaking the sound barrier ) Source moving with vsource > vsound (Mach 1.4 - supersonic) Web link: The Doppler Effect and Sonic Booms

Sonic Boom When the moving object speed reaches Mach 1 (breaking the sound barrier)

Doppler Effect Whistles were put on bombs that were dropped from airplanes in WWII as a means of psychological warfare. When recorded from the plane as a bomb fell, it sounded like this: Why? http://soundbible.com/30-Bomb-Dropping.html http://www.youtube.com/watch?v=cGigkA-Xh5E It was moving away from the plane It was speeding up Both A & B It was falling down It was made to sound like that

Doppler Effect If you were on the ground as a whistling bomb approached you after being released from a plane, what would you hear before the bomb hit the ground? A decreasing pitch (just like we just heard) A constant higher pitch An increasing pitch (reverse to what we just heard) Nothing

Doppler Effect If the source of the sound wave was stationary and you (the observer) were moving past the source, would you observe the Doppler Effect? Yes Yes, but the shift in frequency would go from low to high, instead of high to low No