# Thinking about the Doppler effect as of a boat sailing against the waves!

I can’t believe I haven’t written about this on my blog before, thanks Markus Pössel for reminding me of this great way to understand the Doppler effect!

# Doppler effect, or why ambulances change their sound as they race past you

Doppler shift is everywhere, but it’s maybe not obvious how to imagine what’s going on if you think of sound waves.

But look at the picture below. Can you imagine the sound of those waves lapping against the shore?

Now imagine taking a speed boat riding out on the water. Can you feel how you are bouncing over the wave crests, and notice how you are meeting them a lot more often than when you were standing on the beach, looking out on the water?

Or imagine being a surfer, riding that perfect wave. You are staying with the same wave crest for a really long time, while in front of you creat after crest breaks on the beach.

Yes, the Doppler effect is as easy as this! As you are moving with or against the waves, their frequency changes. Totally obvious when you think about waves on water, right? But the same happens with sound waves, and in their case, a changed frequency means that the sound appears to change pitch. If the ambulance is coming towards you, the sound gets higher and higher, and then as it races away, it gets lower again. So now you don’t even have to look when you hear an ambulance, you know whether it’s coming or going! (Just kidding! Please definitely look out, anyway, and don’t get run over!)

# Simple pendulum

Because physics is everywhere!

Happy New Year, everybody! Hope you all had a good break and are excited to start lots of exciting projects in 2015! One project I will definitely continue working on in 2015 is this blog. It is so much fun to notice physics everywhere!

A friend of mine played music in church on New Year’s Eve, and I was sitting on the gallery, listening. And right in front of me, I saw this (and you’ll need to watch closely in order to spot it!):

Yes, the lamp right in front of the gallery is swinging! We of course remember that the period only depends on the acceleration of gravity and the length of the pendulum. So of course the obvious thing to do is to measure the period and from that calculate the height of the ceiling. Right? Right! Hope you’ll all have as much fun in 2015 as me, spotting science everywhere!