Monday, 29 June 2009

The Doppler Effect Can Cause Pain

In just about every post I've done about our trip to Silverstone I've mentioned (moaned?) that the cars were very, very loud. They were so loud in fact that within a few minutes of them heading onto the track your ears hurt. Strangely though if you had been there you would have found that your right ear hurt more than your left. The reason your right ear would have hurt more than the left can be linked to astronomy and speeding ambulances -- or on other words the Doppler Effect.

We have all experienced the Doppler effect many times. When you hear an ambulance go past with it's siren on I'm sure that you will have noticed that the pitch of the siren changes as the ambulance approaches, reaches and then speeds away from you. This change in the sound is due to the Doppler effect. As sound travels at a uniform speed the sound leaving the ambulances siren is the same, but as it speeds towards you, you hear each wave closer and closer together and then as it passes and moves away from you the waves space out. The same thing happens with the noise from the engine of an F1 car. Just to make things clearer here is a diagram:

Now this diagram isn't totally accurate as a flat out F1 car isn't travelling at the speed of sound, but you should get the idea that the faster the car travels the closer together the sound waves in front of the car become (and the more spaced out behind).

An F1 car is loud even when stationary -- loud enough to hurt your ears if you are too close. The Doppler effect means that as the car is driving towards you that loud, painful sound arrives as lots of closely spaced sound waves yet once it has passed you by the sound waves are spaced much further apart. This explains why at a clockwise circuit such as Silverstone your right ear will be sorer than your left as the cars tend to approach you from the right. Of course if you went to watch a race in Brazil (or any other anti-clockwise circuit) then your left ear would be sorer than your right. The only people with sore left ears at Silverstone would be those on the inside of the circuit and given how much they would have had to pay for their seat or how much money they would have to make to be a guest of one of the teams then I don't have much sympathy for their left ears!

Post a Comment