The Doppler effect is the change in frequency of a wave as its source moves relative to the observer. The same effect that causes the change in pitch of a siren as it drives past is also used to estimate blood flow with ultrasound, measure the speed of a passing car, and even determine the motion of the stars. Doppler shift-based satellite navigation was also the first operational use of a system that eventually led to GPS.

When a siren or similar approaches I try to imagine the crunching up of the sound waves — the vehicle seemingly chasing after its own sound — and the stretching out of the waves as it heads past and into the distance. At least it makes it less painful on the ears.

The Doppler Effect

The often lovely line of interesting seaweed, driftwood and things to find left behind by the waves at the top of high tide. Hopefully, not too much plastic.

More lines: browse line, plimsoll line. draw smooth lines. choose the fast line, the coastline paradox

More beaches: surfing breaks, beaches—amazing for play, gastropods, sea jelly—sea star.

Strand line

Surfing breaks: Beach, reef and point

Common in experience. Less commonly understood.

Sketchplanations tagged with waves