Sound travels—not just through air, but through liquids and solids, too. Your group will listen to a hanger clanged against a table. Then they’ll put their ear to something attached to the hanger to realize that the clanging sound travels through solids, too.
Everything is made of molecules—air, solids, and liquids. Sound starts with a vibration that travels through molecules in waves. The waves are much like the ripples created when you drop a rock into water. When a hanger is clanged on a desk, the hanger and the desk vibrate; creating ripples that travel through molecules in the air and the molecules in the desk. The ripple is the sound wave. Sound waves travel through air at 767 miles per hour. Sound travels even faster through solids because the molecules in solids are more tightly packed together than they are in air. For example, sound travels at 8,859 miles per hour through wood. If you lay your head down on a desk and tap the desk, you will hear the tap both through the desk and through the air. Sound also can travel through liquids, though not as quickly as through solids.
How the human ear hears sounds has to do with vibrations, too. When vibrations hit your ear drum, your brain interprets the vibrations as sound.
Hold the ruler on the edge of the desk and bend down the end that is in the air then let it go. The ruler should vibrate and make a sound. Ask your group some or all of these questions: “What is the ruler doing? Is it making a sound? Can you see it vibrating? Could you feel it vibrating?”
Tell them that all sounds start with an object that vibrates. Ask your group: “Can you name some sounds and think about the object that is vibrating?” Any examples will work but you may want to think of ones your kids can visualize, like the strings on a guitar.
Now ask your group: “How does the sound get from the vibration to your ear?” It travels through the air. “Can sound travel through, say, a desk, or even through water? Do you know how we hear sounds?”
Now pairs of kids can do the activity independently. Give each pair of kids a Sensational Sound activity sheet, a coat hanger, 2 pieces of string, a couple pieces of tape, 2 paper clips, and 2 cups.
As they do the activity, you may want to walk around and make sure the kids are following the instructions and answering the questions on the activity sheet. They may need a little guidance about what is happening: that the sound is traveling through the string and cup to their ears.
When the group is done, ask this question again: “Can sound travel through a solid thing, like a desk?” Let them know that sound can travel through air, solids, and liquids. You may want to give the example that whales communicate with one another by sending sound through the water and ask if they can come up with any other examples.
Have you ever noticed how great your voice sounds when you sing in the shower? Your voice sounds louder and sort of echoes. That's because the sound waves from your voice bounce off the hard surfaces in the bathroom. In this activity, you will make a Hanger Clanger to get a better feel for the vibrations sounds create.