# How Density Affects Sound in Solids, Liquids, and Gases

Density affects sound. Kids in third, fourth, and fifth grade can investigate how it travels through solids, liquids, and gases. If you have a swimming pool, it’s easy. But you can even do it in the classroom!

## Ms. Sneed Teaches How Density Affects Sound

Our favorite fourth grade teacher tapped her pencil on the table. Then she sighed deeply. “We’ve explored five sound energy concepts so far:

“But how can we teach how density affects sound?” she asked her teaching partner.

“That’s a tricky one,” Mr. Frank replied. “When my daughter was in fifth grade, she did a science fair project on that concept. Unfortunately, it required swimming pool.”

### Try It in a Swimming Pool

“Fortunately, the high school swim coach agreed to help us,” Mr. Frank began.

“That day, we picked up Alyssa’s two friends and drove to the high school. After the girls put on their swimsuits, they came out of the locker room and jumped in the pool.

“First, the girls positioned themselves ten meters apart. Alyssa clicked two pennies together, and her friends raised their hands to indicate they heard it. Then they all went underwater, and she clicked the pennies together. Again, they indicated if they’d heard it. Finally, they all swam to the side. Once her two friends had laid their ears against the metal side rail, Alyssa clicked one penny on it. And, of course, they indicated whether they had heard it.”

Mr. Frank chuckled. “Actually, I remember that the girls reacted with surprise when they noise came through the metal side. It was so much louder! They definitely experienced how density affects sound.

“Anyway, this procedure continued with the girls moving farther and farther apart. Of course, the first sound they couldn’t hear was when the pennies clicked in the air. Second, they couldn’t hear sound moving through the water. The girls found that sound travels best through dense solids.”

### You Can Also Explore How Density Affects Sound in Your Classroom

“That sounds like a lot of fun,” Ms. Sneed said. “But how can we show it in our classrooms?”

Mr. Frank rifled through the materials in their sound unit. “Here you go. First, fill three Ziploc baggies with air, water, and sand. Second, kids put the baggies on a table. Laying their heads on each one, they tap the table. Although it doesn’t work as well, our students should notice that the sound is loudest when heard through the solid, second loudest through the liquid, and quietest through the gas.

“Additionally, kids can do the spoon on a string experiment. After you tie the middle of a piece of string to a metal spoon, they wrap the ends around their pointer fingers. Then they let the spoon swing to strike the edge of a desk or table. That gives them an indication of how sound travels through the air to their ears. Next, they stick their fingers in their ears and try it again. Boy, do they get a surprise! The sound is so much louder. Again, sound travels best through solids – in this case, the string. Yes, density affects sound.”

## Enjoy Teaching Sound

Ms. Sneed smiled. “So even if we don’t have a swimming pool, we can show kids how density affects sound. I like these physical science activities. This will be the last of our five science stations for this unit. Let’s get started!”