Doppler Shift Contents: What it is Moving Source Moving observer Whiteboards

Doppler Shift • Contents: • What it is • Moving Source • Moving observer • Whiteboards

Doppler Shift • Demo/examples: race cars, bells at RR crossing • Frequency: (Key to understanding this) • Higher approaching • Lower receding • Moving source/moving observer

Doppler Shift - moving source Sitting Still

Moving to the right Doppler Shift - moving source Source creates smaller wavelengths in front, longer in back Demo - Doppler applet

Doppler Shift - moving source Derivation: ’ =  + usT f’ = shifted frequency f = original frequency v = speed of sound us = speed of source When do you use + and - in the denominator?

Observer Doppler Shift - moving observer Motion of the source makes you experience different frequencies

Doppler Shift - moving observer Derivation:f = v/, f’= (v + uo)/ f’ = shifted frequency f = original frequency v = speed of sound uo = speed of observer When do you use + and - in the numerator?

An airplane with a 62.0 Hz engine flies away from you at 49.2 m/s. What frequency do you hear? (Use v =343 m/s ) (54.2 Hz) You are driving at 29.0 m/s toward a stationary 312 Hz siren. What frequency do you hear?(Use v = 343 m/s) (338 Hz)

Doppler Shift

A man wearing a pointy hat screams at a perfect 1000. Hz while running away from you at 9.5 m/s. What frequency do you hear? (use v sound = 343 m/s) • Source – receding • f = 1000. Hz, us = 9.5 m/s, v = 343 m/s, and + 973. Hz

Your father is nagging you at a pitch of 85.0 Hz, and you ride your motorized “Hello Kitty” skateboard away from him at 14.0 m/s. What frequency do you hear? (use v sound = 343 m/s) • Observer, receding • f = 85 hz, uo = 14 m/s, v = 343 m/s, and - 81.5 Hz

You are running toward the Jo-Jo man with a quarter and a dime at 6.7 m/s. If the music from the truck is at a frequency of 2013 Hz, what is the frequency you hear? (use v sound = 343 m/s) • Observer, Approaching • f = 2013 hz, uo = 6.7 m/s, v = 343 m/s, and + 2052.3 Hz

Duggan is playing the National Anthem on the electric guitar at the senior assembly. You are late, so you are running toward him at 11.2 m/s. If you hear his last note as an A 440 Hz, what is the real frequency he is making? (use v sound = 343 m/s) • Observer, Approaching • f’ = 440 hz, uo = 11.2 m/s, v = 343 m/s, and + 426 Hz

A group of students wearing pointy hats is riding Ducati motorcycles (The “Hello Kitty” limited edition) and chanting “Respectful, Responsible, Safe” driving away from you at 34 m/s. You hear them at a pitch of 512 Hz, what pitch are they really making? (use v sound = 343 m/s) • Source – receding • f’ = 512 Hz, us = 34 m/s, v = 343 m/s, and + 562.8 Hz

A running person who is late for a concert hears the concertmaster who is playing an A 440. Hz. How fast and in what direction are they running if they hear a frequency of 463 Hz. (use v sound = 343 m/s) Moving observer, toward, use + 17.9 m/s, toward the source

What speed in what direction is a car moving if it has a 256 Hz horn, but you hear it at 213 Hz? (use v sound = 343 m/s) Moving source, away, use + 69.2 m/s away from you

You are driving on a road, and a car coming the other way has a horn with a frequency of 256 Hz. The oncoming car is going 20.0 m/s toward you, and you are going 60.0 m/s toward them. What frequency do you hear? • Moving source, then moving observer • higher frequency, higher frequency • f’ = f{ v } • {v + us } • f = 256 hz, us = 20.0 m/s, v = 343 m/s, and - • f’ = f{v ± uo} • { v } • f = f’ from before, uo = 60.0 m/s, v = 343 m/s, and + 319.4 Hz

A car with a 256 Hz horn approaches you at 40.0 m/s. What frequency do you hear? (3) (use v sound = 343 m/s) • Moving source • higher frequency • f’ = f{ v } • {v + us } • f = 256 hz, us = 40.0 m/s, v = 343 m/s, and - 290. Hz

Doppler Shift Contents: What it is Moving Source Moving observer Whiteboards