# Sound Energy and Materials

In this unit, students build on their exploration of how energy and matter interact with a focus on science phenomena related to sound. In this lesson, students investigate how some materials absorb sound while others reflect it. This page is a high-level extract of this lesson.

## Science Background for Teachers:

The science background section gives teachers more in-depth information about the phenomena students explore in this unit on matter and sound. Here is an excerpt from the science background information on sound energy and materials.

In a sound wave, the distance from one compression to the next or from one rarefaction to the next is the wavelength. A wavelength is the distance spanned by one cycle of the motion of a wave. The frequency of a wave is the number of waves that pass a set point in a given amount of time. When a sound wave has a high frequency, it produces a high-pitched sound, such as a flute. When a sound wave has a low frequency, it produces a low-pitched sound, such as a drum.

Amplitude is a measure of a wave’s displacement from its resting position. Displacement refers to the movement of a substance from its resting position. The vibrating molecules in a sound wave are more compressed when the wave has a greater amplitude and less compressed when the wave has less amplitude. Amplitude is also related to a sound’s volume because a wave with a greater amplitude has more energy. When a sound wave has a greater amplitude, it produces a louder sound.

As sound waves move through matter, they continue in a straight line until they come into contact with a different medium, which changes their motion. There are different ways that a wave can behave after this interaction, but this unit focuses on three: transmission, reflection, and absorption.

When a sound wave is transmitted through a material, it passes through and the sound is heard on the other side. When a sound wave is fully absorbed by a material, the energy is converted to heat and no sound is heard on the other side. Finally, when a sound wave is reflected by a material, it bounces off of the material or substance. If the sound wave is fully reflected, it will bounce back into your ears. This is what happens with an echo.

There are a couple of things that need to happen for echoes to occur. The first is that there has to be a material for the sound waves to reflect off of, rather than being absorbed or transmitted through. Harder, smoother materials tend to be more reflective, while softer, rougher materials tend to be more absorbent. This is what happened with the famous new paint in Jordan Hall in Boston, MA. It was smoother and therefore more reflective than the old, more porous paint.

The second important factor for creating echoes is space. Sound moves very quickly, but it still takes time for the energy to move from one place to another. Echoes happen when there is a break between when you hear the original sound and when you hear the reflected sound. Finally, the sound needs to be loud enough so that it has enough force to move through the large space and back.

The world record for longest echo was held for more than 40 years by a slammed door in Hamilton Mausoleum in Scotland. It took 15 seconds for the sound to stop echoing. The sound waves produced by the slammed door traveled through the air until they collided with the smooth stone walls and a high dome reaching a height of about 37 meters (123 feet). They then reflected off of the walls and ceiling to produce the echo.

Gymnasiums are also known for producing echoes because they are large rooms with hard, smooth materials on the floor, walls, and ceilings. In contrast, libraries are designed to absorb sound to keep the rooms as quiet as possible.

## Science Lesson: Exploring Sound Energy and Materials

Once students understand how sound energy is transferred in waves, they explore, in this lesson, how sound waves interact with different kinds of matter as they observe how much sound energy is transmitted and absorbed by different materials.

## Science Big Ideas

• Sound is energy carried by vibrating molecules.
• Sound waves that come into contact with a different medium can be absorbed, reflected, or transmitted.
• Acoustics refers to the properties of a space that determine how sound waves travel, and it includes the shape of a room and the materials that make it up.

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## Science Essential Questions

• How does sound travel from one place to another?
• Why can't we hear any sounds when sound waves are fully absorbed into a material?
• What happens to sound waves when they are fully reflected from a material, rather than transmitted?
• What materials are more likely to reflect sound waves?
• What happens when sound waves are partially absorbed and partially transmitted through a material?
• How do you think the sound in a gymnasium would sound compared to the sound in the concert hall?
• Why do most concert halls have carpet, and how this might affect the sound compared to a gym?
• How does the thickness of a porous material affect how much sound energy it absorbs and transmits?

## Common Science Misconceptions

Misconception: Sound energy moves in the empty space between particles of matter.
Fact: Sound energy moves by vibrating molecules that collide with one another, passing on the energy from one molecule to another.
Misconception: Sound moves faster in air than in liquids or solids because air forms less of a barrier.
Fact: Sound moves fastest in solids and slowest in air because the molecules of solids are more closely packed together, so the sound can transfer from one molecule to the next more quickly.

## Science Vocabulary

Absorb : to take in

Acoustics :  the properties of a space that determine how sound waves travel

Amplitude :  a measure of a wave’s displacement from its resting position

Frequency :  the number of waves that pass a set point in a given amount of time

Reflect :  to bounce off of

Sound :  energy that is carried in waves by vibrating molecules

Sound Wave :  a pattern of vibrating molecules caused by the movement of sound through a medium

Transmit :  to pass through

Vibrate :  to move back and forth quickly

Wavelength :  the distance spanned by one cycle of the motion of a wave

## Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

Renovating a Concert Hall

Jordan Hall is part of the New England Conservatory, located in Boston, Massachusetts. It is considered one of the United States’ best performance spaces because of its acoustics.

Acoustics are the properties of a space that determine how sound waves travel. It is important when designing buildings such as auditoriums, theaters, and libraries.

In 1995, Jordan Hall was renovated. To renovate means to make repairs. These renovations were done carefully to keep the acoustics of the hall. No structures of the room were changed that might affect how sound was carried.

But the first night musicians played after the renovations, the music sounded different. Many people said it sounded too “bright.” Some audience members covered their ears with their hands.

How Materials Absorb Sound

It turned out that the new paint may have had a role to play in the changed sound. The new paint wasn’t as porous as the old paint. This means it didn’t have a lot of spaces between its particles.

It’s possible the new paint was much more reflective than the old paint. As the musicians played, their instruments made vibrations. These vibrations moved through the air in sound waves. As the waves came into contact with the painted walls, they were reflected back.

The more porous paint absorbed more of the sound waves. To absorb means to take in. When a sound wave is fully absorbed into a material, all of the sound energy transfers to the material and is changed to another form, such as heat. When this happens, no sound is transmitted through the material.

Many materials absorb some, reflect some, and transmit some sound energy. It depends on the properties of the material, including how porous it is and how thick. When sound waves are partially absorbed and partially transmitted, some of the sound is carried through the material, but it isn’t as loud because some of the energy has been converted to another form.

Acoustics of a Room

The old paint of the concert hall absorbed more of the sound waves than the new paint did. This resulted in a softer sound. After a year, the concert hall added felt cloth to its walls. This returned the acoustics to the previous sound because felt is more absorbent than the new paint. In general, softer, rougher materials tend to be more absorbent. Harder, smoother materials tend to be more reflective.

Concert halls like Jordan Hall are designed so that everyone in the room can hear the music. One way these halls achieve this is their shape. They are often designed with many curves that move the sound around the room.

Concert halls also have carpet to absorb sound energy. This transfers the sound energy into heat and prevents echoes.

Libraries have a different acoustical design goal. Libraries are designed to keep sound from traveling to help them stay quiet.

## Hands-on Science Activity

In this lesson, students figure out the relationship between the thickness of different porous materials and the amount of sound energy those materials absorb and transmit. Students experiment with the phenomena of vibrating particles and develop evidence for how much sound energy transmits through material. Students use their experimental data to form conclusions about how sound energy interacts with different materials depending on their properties.

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