99 Seeing Sound-Mid

Seeing Sound FOCUS Question What would different sounds look like if people could see them?

What's That Sound? Tap a spoon against a glass of water. Small particles, called molecules, in the glass vibrate. The vibrating molecules touch other molecules of water and air. This makes them vibrate, too. The vibrations go in all directions. Some of the vibrations travel into people's ears and vibrate their eardrums. The ears send signals to the brain. That's how people hear the sound clink! Sound is a vibration that travels through matter and can be heard. But what would sound look like if people could see it?

How We See Sound Hold a rubber band sideways between your thumb and finger. Then pluck it with another finger. The rubber band vibrates. Each time the rubber band moves up, nearby air molecules are compressed, or squeezed together. Each time the rubber band goes down, those same air molecules spread out. This motion happens over and over. These vibrations create a sound wave. You might hear a boing! People can't see sound waves moving through the air like they can see waves in the ocean. But we can use technology to measure how tall each sound wave gets and how far apart the waves are. Then, by graphing the results people can "see" the sound.

What Sound Looks Like People use special equipment that turns sound waves into a graph of wavy lines called a waveform. The waveform shows the shape of sound waves. The top point of the wave is called the crest and the bottom point is called the trough (rhymes with "off"). A waveform has many crests and troughs. Sounds can be quiet, like a fluttering leaf, or loud, like a clanging bell. They can be low like a growling bear, or high, like a squeaking mouse. Since sounds are different each waveform looks different.

Get Amped About Amplitude Loud sounds, like blasting music, have a lot of energy. Many people can hear and even feel the vibrations. Turn the radio down, and there is less energy. Amplitude is the height of a sound wave from the top of the crest to the bottom of the trough. It describes the amount of energy in a sound. Loud sounds have high amplitude, so the waves look tall. Quiet sounds have low amplitude, so the waves look shorter. Word Wise You can amplify sound using an electric amplifier, or amp. This increases the volume of the sound and the amplitude of the sound waves.

Pitch-Perfect Frequency Frequency measures the speed of a vibration. It counts the number of waves that pass a point in one second. We measure frequency in units called hertz (Hz). People hear the frequency of sound waves as pitch, or whether a sound is high or low. Slow vibrations produce waves that are farther apart, with low frequency. The sound has a low pitch. Fast vibrations produce waves with high frequency. The sound has a high pitch. Both low- and high-frequency sound waves move fast. For example, human speech makes sounds with waves that move between 100 and 16,000 hertz. Do You Know? Sounds that have random frequencies are called noise. These waveforms look jagged.