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Comparing how sound moves through solids, liquids, and gases like air and water.
Have you ever wondered why you can hear a train coming by putting your ear to the metal track long before you hear it through the air?
Sound is actually a vibration that travels by bumping into molecules—the tiny building blocks that make up everything! In a gas like the air around us, these molecules are spread far apart, like kids playing tag in a giant field. Because they are so far apart, it takes a long time for one molecule to bump into the next one to pass the sound along. This is why sound travels the slowest through the air, moving at about meters per second.
Quick Check
Why does sound travel the slowest through gases like air?
Answer
Because the molecules in a gas are spread far apart, making it harder for them to bump into each other and pass the vibration.
In liquids like water, the molecules are much closer together than in air. Imagine a crowded swimming pool where everyone is standing just an arm's length apart. If you push one person, they quickly bump into the next. Because the molecules are closer, sound travels about 4 times faster in water than in air! This is why whales can 'talk' to each other across huge distances in the ocean.
1. Imagine you are at a pool. 2. If your friend claps their hands in the air, you hear a normal 'pop.' 3. If you both go underwater and your friend claps, the sound is much louder and sharper. 4. This happens because the water molecules are closer together, carrying the vibration to your ear more efficiently.
Quick Check
If sound travels m/s in air, and it is 4 times faster in water, roughly how fast is it in water?
Answer
About meters per second.
In solids like a wooden door or a metal pipe, molecules are packed tightly together. They are like people standing shoulder-to-shoulder in a line. When a vibration starts, the molecules bump into each other almost instantly. Because of this 'tight packing,' sound travels the fastest through solids. In steel, sound can travel at a speed of meters per second! That is nearly times faster than in air.
1. Take two paper cups and connect them with a long string. 2. Pull the string tight so the molecules in the string are pulled close together. 3. When you whisper into one cup, the vibration travels through the solid string. 4. The sound is much clearer than if you just whispered through the air because the solid string is a better 'highway' for sound.
Imagine a race between three sound waves starting at the same time over a distance of meters: 1. The wave in the Air takes about seconds. 2. The wave in the Water takes less than second. 3. The wave in the Steel Rail takes only seconds! 4. The solid wins because its molecules never have to 'run' far to bump into their neighbors.
Through which of these materials would sound travel the FASTEST?
Why can whales hear each other from far away?
Sound travels about 15 times faster in steel than it does in air.
Review Tomorrow
Tomorrow morning, try to remember the 'Shoulder-to-Shoulder' rule: Why does being close together help molecules pass sound faster?
Practice Activity
Find a long wooden table. Have a friend scratch one end very softly while you listen through the air. Then, put your ear against the wood and have them scratch again. Notice the difference!