Why does a police siren change its note as it races past you?
Show of hands — before you project anything
Predict first: if the siren drives toward you, will the waves reaching your ear be squished closer together or spread further apart? Then watch and check.
A Way more than you'd guess
B About what you'd guess
C Way less than you'd guess
Count the votes out loud. Hold them to it — then watch.
Predict first: if the siren drives toward you, will the waves reaching your ear be squished closer together or spread further apart? Then watch and check.
Why does the pitch drop the exact instant the siren passes you, instead of changing slowly?
A parked siren and a moving siren both play the same note. Predict which one tells you it just went by, and explain why.
Where it shows up in real life
An ambulance or police car racing past on the street
The ice-cream truck or a motorbike zooming by
A race car or train horn blasting past at a track or crossing
Why does a police siren change its note as it races past you?
Predict — what do you think will happen, and why?
Draw what you saw
Talk about it
Predict first: if the siren drives toward you, will the waves reaching your ear be squished closer together or spread further apart? Then watch and check.
Why does the pitch drop the exact instant the siren passes you, instead of changing slowly?
A parked siren and a moving siren both play the same note. Predict which one tells you it just went by, and explain why.