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Exploring how the speed of vibrations changes the pitch of the sounds we hear.
Have you ever wondered why a tiny kitten's meow sounds like a squeaky toy, while a giant lion's roar sounds like a deep, rumbling thunderstorm?
When we talk about sound, we often think about how loud it is. But there is another important part of sound called pitch. Pitch is how high or low a sound is. Think of a whistle—it has a very high pitch. Now think of a heavy bass drum—it has a very low pitch. Pitch is not about volume; a whisper can have a high pitch, and a shout can have a low pitch!
Quick Check
If you are listening to a squeaky mouse, are you hearing a high pitch or a low pitch?
Answer
A high pitch.
Every sound is caused by vibrations, which are fast back-and-forth movements. The secret to pitch is how fast something vibrates. If an object vibrates very quickly, it creates a high-pitched sound. If it vibrates slowly, it creates a low-pitched sound. We can measure these vibrations in cycles per second. For example, if a string vibrates times in one second, it sounds higher than a string vibrating only times in one second.
1. Take a thin rubber band and stretch it between your fingers. 2. Pluck it and watch it move. It moves very fast! 3. Because it vibrates quickly, you hear a high pitch. 4. Now, take a very thick, loose rubber band and pluck it. It moves slower, creating a low pitch.
Quick Check
Does a fast vibration create a high pitch or a low pitch?
Answer
A high pitch.
The size of an object usually changes its pitch. Smaller objects tend to vibrate faster, which is why a small bell has a higher pitch than a big one. Think about a flute versus a tuba. The flute is small and short, so the air inside vibrates quickly ( pitch). The tuba is huge and long, so the air vibrates much slower ( pitch).
1. Take two identical glass bottles. 2. Fill one almost to the top with water and leave the other mostly empty. 3. Blow across the top of the bottle with more water. The space for air is small, so the air vibrates fast, creating a high pitch. 4. Blow across the mostly empty bottle. The air has more room to move, vibrates slower, and creates a low pitch.
Imagine a piano. Inside, there are many strings. 1. To make the highest note, the piano uses a string that is very short and very thin. 2. To make the lowest note, it uses a string that is long and wrapped in thick wire. 3. If the short string vibrates at Hz (vibrations per second) and the long string vibrates at Hz, the short string has the higher pitch because its frequency () is much larger.
Which of these describes a high-pitched sound?
If an object starts vibrating faster than before, what happens to the pitch?
True or False: A big tuba has a lower pitch than a small flute because it is larger and vibrates more slowly.
Review Tomorrow
In 24 hours, try to remember the 'Rubber Band' rule: Does stretching it tighter make the pitch go up or down?
Practice Activity
Go on a 'Pitch Hunt' around your house. Find one object that makes a high-pitched sound and one that makes a low-pitched sound, then explain to someone why their vibrations are different speeds.