The speed of sound - what is it?
Well our friend (really my uncle) Dr. Hertz will help us to learn more about sound.
"As I was saying in the previous section Wizard, the speed of sound is a real neat thing to study. I guess the best known example of this neat phenomena are fireworks. Most of you know that when you see fireworks, you see the explosion before you hear the sound. That's because light travels much faster than sound. So the light reaches your ears before the sound reaches your ears. Now, the speed of sound isn't always the same. If you observed a fireworks display in hot temperatures, and then in cold temperatures, you would notice a difference in time of sound arrival. Likewise, if the same fireworks display were conducted in say Helium (Not a very good idea) as opposed to the air in our sky, the sound would each our ears much quicker. Now this explains the phenomena we hear when someone swallows some Helium - their voices become a lot higher. That's because sound travels faster in helium than in regular air, in this case the air being in the throat of the person."
"Wow Uncle Hertz, that's pretty good. Well Uncle, Dr. Hertz, maybe you could tell us about why some planes make so much noise!"
"Nooooo problem. Well you see young Willy, when planes travel faster than the speed of sound (possible with very fast engines) they generate an interference pattern behind them. Why? The plane is traveling faster than it makes noises. Anyway, this interference is not good for the faint of ears, as the sound is very, very loud. If you can hear a plane to be so loud from the ground, imagine how loud it is up by the plane!"
"Ah ha. Very interesting. Perhaps you could tell me more. When an ambulance approaches, you can hear it getting louder and louder, then as it passes you, the sound gets less and less?"
"That's a good question. Well we call this the Doppler Effect. If you've noticed, when someone screams from far away, you can't hear them that well. But, when they scream from up close, you can hear them very well. The sound waves become compressed as the ambulance approaches you. This increases the frequency of the waves, which you hear as an increase in the pitch of the siren. When the ambulance passes and starts moving away from you, the sound waves become stretched. This decreases the frequency of the waves, which you hear as a decrease in the pitch of the siren."
"Wow! I never knew that before! Well Uncle, I mean Doctor Hertz, thank you for your time and I'll see you at the next family reunion."
"Yah, well I'll only talk to you if you don't wear that hideous hat of yours Who do you think you are! Jamiroquai??"
Relatives! In our next page, we will find out about some cool characteristics of waves. So click below to find out more!"
Sound travels at the speed of sound, surprise! (331 m/s)
The sound phenomena we hear when an ambulance passes us by is known as the Doppler Effect
Characteristics of waves