Sound Waves

Noise is caused by sound waves, which are just molecules vibrating. A sound wave is a longitudinal wave, which means that it oscillates in the same direction as it moves. A sound wave can travel in ONLY matter because it needs to transfer its energy from molecule to molecule. So, if you send your alarm clock to outer space, which is a vacuum, it wouldn’t make a sound.

Speed of sound: Sound waves travel much more slowly than light waves--about 340 meters per second. That’s why you see distant lightning before you hear its thunder. Although light waves travel slowest in solids, sound waves travel fastest in solids. Molecules are closer together in solids, so the molecules can bump into each other faster and transfer sound waves more quickly.

Intensity of sound: The intensity of a sound wave is how much energy the sound wave carries. The amplitude of the sound wave causes the intensity--the larger the amplitude, the higher the intensity and the louder the sound. The intensity of a sound wave decreases as you get farther away from the sound’s source, which is why things sound quieter at a distance. As the waves travel, their energy gets absorbed by the air and other objects.

The loudness, or intensity, of sound is measured on the decibel scale (dB).

Pitch: When you listen to a song, you hear many different tones. The different tones we hear are related to the sound’s frequency, or the number of vibrations per second. Higher sounds have higher frequencies(short wavelengths), and lower sounds have lower frequencies(long wavelengths). Our perception of sound wave frequency is called pitch.