Sound, acoustic waves, resonance, and acoustic phenomena. Musical genres belong in Music Genres; instrument identity and construction belong in Musical Instruments.
Test your knowledge with these top questions!
During a Doppler shift, what happens to a siren sound's speed through unchanged, still air?
The moving siren bunches sound waves together or spreads them out without speeding up or slowing down the waves.
A siren sounds lower after an ambulance passes. Which effect explains the pitch change?
The siren can keep playing the same note while motion changes the frequency that reaches your ears.
A cyclist rides toward a stationary, steady-note siren. How does the cyclist hear its pitch?
A moving listener meets sound wave crests more often even when the source does not move.
Doppler ultrasound measures which property of blood moving through a vessel?
Moving blood cells reflect sound with a shifted frequency, helping doctors find narrowed or blocked vessels.
Active noise-cancelling headphones reduce unwanted noise by producing what?
A pressure rise in the unwanted wave meets a pressure drop in the added wave, reducing the vibration at the ear.
Which speed marks the threshold for an aircraft to create a sonic boom?
Sound travels faster through warm air, so the speed needed to fly supersonically changes with air temperature.
How does a steady siren's pitch change when an ambulance goes from approaching you to moving away?
Behind the ambulance, sound waves spread farther apart, so fewer reach your ears each second.
Which effect makes a passing ambulance's steady siren seem to change pitch?
The effect also shifts light from moving objects, helping astronomers tell whether stars approach or recede.
With length and tension unchanged, plucking a string harder mainly changes which sound property?
A harder pluck makes the string swing farther sideways, sending stronger pressure changes into the air.
At the same length and tension, why does a thicker steel string make a lower pitch?
Wrapping dense wire around a string adds mass, allowing a lower pitch without needing a longer string.