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Learning about amplitude and how the amount of energy affects the loudness of a sound.
Why can you hear a drum from across a giant playground, but you have to lean in close just to hear a friend's whisper?
When we talk about how loud or quiet a sound is, we are talking about volume. Think about the remote control for a TV. When you press the 'plus' button, you are increasing the volume to make the sound louder. When you press the 'minus' button, you are decreasing it to make it softer. Volume is all about the strength of the sound reaching your ears. It is different from pitch, which is how high or low a sound is. Even a very high-pitched whistle can be either very loud or very soft!
Quick Check
If you turn down the sound on a radio so it is hard to hear, are you changing the pitch or the volume?
Answer
You are changing the volume.
Every sound starts with a vibration, which is a quick back-and-forth motion. To make something vibrate, you need energy. The amount of energy you use determines the volume. If you hit a drum with a lot of force (high energy), the drum skin moves up and down a long way. This creates large vibrations. These large vibrations push the air harder, creating a loud sound. If you tap the drum lightly (low energy), the vibrations are small, and the sound is soft.
1. Place your hand flat on your desk. 2. Use one finger to tap the desk very gently. This uses a tiny amount of energy (). 3. Listen to the soft sound and feel the tiny vibration. 4. Now, use your whole hand to knock firmly on the desk. This uses more energy (). 5. The sound is much louder because the vibrations are bigger!
Quick Check
What kind of vibrations create a loud sound: large vibrations or small vibrations?
Answer
Large vibrations create loud sounds.
Scientists use the word amplitude to describe the size of a vibration. You can imagine sound vibrations like waves in the ocean. A giant wave that towers over a boat has a high amplitude and carries a lot of energy. A tiny ripple in a pond has a low amplitude and very little energy. In the world of sound, high amplitude means a loud volume, and low amplitude means a soft volume. The more energy you put in, the higher the amplitude of the vibration!
1. Stretch a rubber band between two fingers. 2. Pull the string back just a tiny bit ( mm) and let go. The vibration is small, and the sound is soft. 3. Now, pull the string back much further ( mm). You are using more energy to stretch it. 4. When you let go, the rubber band moves back and forth a greater distance. The amplitude is higher, and the sound is much louder.
Think about a storm. A single raindrop hitting a window uses a tiny amount of energy, creating a soft 'plink.' However, a lightning bolt heats the air so fast it causes a massive explosion of energy. This creates a vibration with huge amplitude that we hear as thunder. The difference in volume is because the energy in thunder is millions of times greater than the energy in a raindrop!
Which of these is the best definition of volume?
If you want to make a louder sound on a piano, what should you do?
True or False: Large vibrations have more energy than small vibrations.
Review Tomorrow
Tomorrow morning, try to explain to someone why hitting a drum harder makes a louder sound using the words 'energy' and 'vibration'.
Practice Activity
Find three objects at home (like a plastic tub, a spoon, or a bell). Try to make the softest sound possible with each, then the loudest. Notice how much more effort (energy) your muscles use for the loud sounds!