What Is Pitch?
Find out what the pitch of a sound is and what causes that pitch.
Goal:
Goal:
Sound waves are compression waves, but they are often represented as transverse waves when discussing their patterns of motion. The wavelength is the distance between a point on a wave and the same point on the next cycle of the wave.
Sounds are often described by how loud or soft they are. The loudness of a sound is related to the amount of energy that is then carried by the sound wave. The amplitude of a wave is directly related to energy, which means that the higher the amplitude, the higher the amount of energy being transferred. Think back to the demonstration with the walking spring toy. If you shake it gently, the wave will have a small amplitude. If you move the slinky in larger movements, the wave will have a greater amplitude.
Sounds are also described as how high or low they are. This is called the pitch of the sound. The pitch is determined by how fast the sound vibrations move. Animals can hear sounds at different pitches. Click through the slides to learn more.
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Think back to the demonstration with the walking spring toy. When you jerked the toy back and forth repeatedly, you created a series of compression waves. When you went really fast, the vibrations you created moved faster. You might have noticed that you could go even faster if you made your hand movements smaller. 
This is the same way the vibrations determine pitch. A sound wave that is vibrating slowly is a low-frequency sound wave. It has a lower pitch. A wave that is vibrating very fast has a high frequency and a higher pitch. It's challenging to measure the frequency ranges for different animals. Humans can hear sounds from a frequency of about 20 vibrations per second up to about 20,000 vibrations per second. That's a wide range! These units of frequency (vibrations per second) are called hertz. When you hear that a sound has 200 hertz, it means the waves are vibrating 200 times each second. Other animals have very different hearing ranges. Dogs can hear sounds at much higher frequencies than we can—well over 30,000 hertz! That's why some dog whistles and dog fences use high-pitched sounds: The sounds won't disturb people, but the dogs will respond. Dolphins can make and sense sounds at extremely high frequencies—about 150,000 hertz. Some whales give off low-frequency sounds that can travel through the water for hundreds of miles. Whales have extremely sensitive ears that can sense these sounds over long distances. Elephants can also use very low-frequency sounds—much lower than we can hear—to communicate with each other!
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