hcho15.html

		l Iike to sing in the shower because my voice sounds extra loud and it kind of echoes. ALEC, our supercomputer, told me that this happens because the sound waves from my voice bounce off the hard surfaces in the bathroom.

		Sound waves must bounce a lot in the halls in my building, too, because my footsteps always sound extra loud when I walk through.

ALEC says sound can bounce off solid things, and it can travel through them, too.

Let's find out what he's talking about!


	2 pieces of kite string
	a metal coat hanger
	tape
	2 paper clips
	2 paper or plastic cups

	Cut 2 pieces of string, each about 2 feet (60 cm) long.
	Attach each string to a paper cup. First, tie a paper clip onto an end of each string. Then, poke a hole in the bottom of each cup with a ballpoint pen, and thread thread the string through. The paper clip should be on the inside.

	Tie the other ends of the strings to a hanger, and tape each knot in a corner.
	Hold the cups and clang (hit) the hanger against a desk or a table a couple of times.
	*What sound do you hear?* *Can you see or feel the hanger vibrating?*

	Now, hold the cups up to your ears. Bend at the waist and clang the hanger again. Be sure you keep the cups on your ears while the hanger hits the desk.
*What sound do you hear now?* *Is it the same sound you heard the first time?* *If not, what do you think made the difference?*

Sound is vibration. When something vibrates (shakes), it moves the air molecules around it and makes sound waves.

Sound waves travle through gases (like air), solids and liquids.

The speed of sound is super fast - sound waves travel about 767 miles per hour through the air!

But sound is different depending on what it travels through. Try clinking together two pieces of silverware in the air. Now, touch one piece of silverware to a table and clink the other one to it. Is the sound different?

You can try this experiment with other objects, too.