Well here we are. With a little help from our friend Doctor Hertz, we will learn more about the neat properties of sound. There's our friend right now.

"Hi Dr. Hertz!"

"Hi everybody!"

"So Dr., can you tell us about some of the neat properties of sound?"

"Of course, you know I did learn something at the upper Hollywood actor/doctor college. Now what do you hear when you think of sound? Sound I hope, but what do you really hear?"

"I hear everyone saying 'What a horrible hat!!' 'Can't you put anything better on?'"

"Not you silly, I mean the person who is visiting this web page! Well I'm guessing when you think of sound you probably think of echo. Echo is one of the most interesting phenomena of sound. When you hear echo, It doesn't mean that someone else with exactly the same voice is calling out to you with exactly the same phrase. What it is, is reflection of sound.

I'm sure everyone's familiar with mirror reflections. Well similarly, sound can bounce off of objects and reflect better in some materials that others. When you are in an open room or in a mountainous valley or when you scream, your voice vibrates the air around you, and the vibrations in the air vibrate all the air around you. But when these vibrations in air encounter say a mountain or a wall, some of the sound gets absorbed into the wall, and some gets reflected back.

And guess what, the reflection is almost always reflected in your general direction, so you hear your voice again after you have vibrated the air, the air vibrates a wall, the wall vibrates the air again, and the air vibrates your ears. Think of the process as you throw a tennis ball against a wall."

	Click here for sound
This is what an echo looks like	This is what an echo sounds like

"Wow Dr. Hertz, it's like you've known me all my life. Thank you."

"Your welcome - and Wizard, I have known you all your life, I'm your uncle!! And by the way, when did you become a wizard, we always used to call you William when you were little…"

"Ah ha, uham, lets forget my childhood for now. Maybe you could tell us more about sound phenomena."

"No problem! Well I guess another really neat thing about sound is its speed. To find out more about the speed of sound click below"

"Hey that's my line - 'To find out more about speed, please click below'"

An echo is a reflection of sound of an object. It's like playing tennis

The speed of sound