To investigate the work of the scientist Ernst Chladni and to replicate his experiment showing the movement of sound.
Ernst Chladni, an 18th century German scientist and musician, was a pioneer in the field of acoustics, the science of sound. In a famous experiment, he showed how moving a violin bow against a metal plate covered with sand could visually display the movement of sound. The sand concentrated in areas where the plate was not vibrating. Through this work, Chladni concluded that sound travels in waves. He was the first scientist to clearly demonstrate this connection.
During the lesson, students will duplicate Chladni's experiment or watch and participate in a teacher demonstration. Students will begin the lesson by watching the short video from the National Museum of American History (NMAH) entitled Introduction to Acoustics Instruments. This video will give students an overview of what acoustics is and how different instruments from long ago illustrate different principles about sound.
During the Development phase of the lesson, students will focus on one particular instrument—the Chladni plate. Before beginning the activity, students should watch a second video in the NMAH series, Chladni Plate Demonstration. Working in small groups of five, students will re-create this experiment or participate in a teacher demonstration. Each group will be given a metal plate, salt, and a bow. They will run the bow against the plate over five trials. For each trial, they will draw the pattern the salt makes. After completing their trials, students will discuss what the different patterns illustrate about the movement of sound.
Sound is a difficult topic for many students to understand, and they often have misconceptions about it. This activity will address the misconceptions, as identified in Children’s Misconceptions about Science:
- Sound moves faster in air than in solids (air is "thinner" and forms less of a barrier).
- Sound moves between particles of matter (in empty space) rather than matter.
- As waves move, matter moves along with them.
When introducing the topic, try to ask questions that will help you determine if your students have these misconceptions.
To prepare for this lesson, watch the two videos from NMAH: "Introduction to Acoustics Instruments" and "Introduction to the Chladni Plate," both of which can be found at The Science Teaching Collection: Acoustics. You should us Windows Media Player to view these videos. The second video explains the main concepts of the lesson, which are:
- When Chladni bowed the metal plate covered with sand, beautiful patterns emerged.
- The places where the sand did not collect show how far sound waves moved the sand.
- The places where the sand did collect represent nodes between waves. A node is the point of zero amplitude, meaning the particles at those points were not moved by waves.
- Chladni was the first scientist to clearly demonstrate the connection between sound and waves, paving the way for the acoustical theory of waves.
To prepare for the experiment performed in this lesson, make sure you have a violin or cello bow ready for each group to use. The bows should be very tight and well rosined. It also would be best to have plates that are attached to a pole or some kind of screw.
If you have trouble finding enough bows or plates for each group, consider doing this activity as a demonstration. After showing students how to bow the plate, students can be given a turn to try to do it themselves. Make sure you conduct at least five trials and that students have time to fill out the What Patterns Do You See? student sheet.
Begin the lesson with a quick discussion about sound. To find out what students know about the topic, ask these questions:
- How would you describe sound?
(Students may respond by saying that sound can be unpleasant, like a noise, or beautiful, like music. They also may mention that sound may be loud or soft, high or low.)
- How does sound travel?
(See if students know that sound travels in waves.)
- What causes sound?
(See if students know that sound can be caused by tapping an object, running a bow over it, plucking strings, or creating a vibration in any other way.)
- What materials can sound travel through?
(See if students know that sound can travel through solids, liquids, and air.)
Record students' responses on a sheet of newsprint. If their answers reveal any misconceptions about sound, try to address them throughout the lesson.
Next, students should use their Exploring Sound Waves student esheet to go to and watch the Introduction to Acoustics Instruments video. After watching the video, students should answer these questions on the Exploring Sound Waves student sheet:
- What is acoustics?
(Acoustics is the study of the physical nature of sound.)
- Why were ancient peoples interested in sound?
(They were interested in sound because of their interest in music, as well as because of their desire to improve the quality of sound in buildings.)
- What did early scientists think sound was?
(Early scientists compared sound to a wave found in the water, but they really didn't understand it much more than that.)
- What did tuning forks illustrate?
(They demonstrated the interaction of sound waves.)
- How has the study of sound changed?
(The study of sound has changed in that it is no longer a mechanical science. Now it is an electrical science and includes microphones, speakers, and other devices used to improve acoustics.)
Next, students will either conduct Chladni's experiment or watch a demonstration. If you decide to do the demonstration, make sure that some students have a chance to bow the plate to see how the salt moves.
Note: The following instructions are for the student groups. If you are doing a demonstration, you need to have just one set-up.
Divide students into groups made up of approximately five students. Give each group a metal plate attached to a screw, a clamp, and a violin or cello bow. Have the box of salt available so that students can access it when they are ready.
Next, students should use their esheet to watch the Introduction to the Chladni Plate video. Tell students that they will either duplicate this experiment or watch you demonstrate it.
There are many different ways to conduct this experiment. Students can use their esheet to check out these sites to see other ways of doing this experiment:
Hand out the Chladni Plate Experiment student sheet. If applicable, tell students to follow the directions on the sheet. For your information, these steps are listed below:
- Attach the metal plate to a desk with the clamp. Make sure the desk is not wobbly and the plate is securely attached. If necessary, put index cards underneath the legs of the desk to make sure it doesn't move.
- Sprinkle a generous amount of salt on the metal plate.
- Run the bow along the rim of the plate as you saw demonstrated in the video. Note the pattern that is made. Then draw the pattern on the What Patterns Do You See? student sheet.
- Conduct five trials. After each trial, draw the pattern on the sheet. Make sure that each member of your group has a chance to bow the metal plate.
Make sure the groups clean up after they finish the experiment and complete the What Patterns Do You See? student sheet. Tell students that they should have their sheets available for the upcoming class discussion.
Bring the class together as a group and have a discussion about the activity. To see what students have learned and whether their misconceptions have been addressed, ask these questions:
- How does sound travel?
(Sound travels in waves.)
- Can sound travel through solids?
(Yes, the patterns created by the salt on the metal pan indicate how the sound waves are traveling in response to the vibrations created by the bow.)
- Based on what you learned during the lesson, do you think that sound can travel through liquids? How could you show this idea?
(Sound can travel through liquids. You can test this idea by blowing into a glass of water. You will notice that the water moves, indicating that the vibrations you made caused this movement.)
- Do you think that sound can travel through air? If so, why?
(Yes, sound can travel through air. You know that it is does because you hear sounds all the time, from the chirping of birds to the loud sound of a jackhammer to the sound of people's voices.)
- Did the solid metal plate destroy the sound waves?
(No, the pattern made by salt indicates that the sound waves are intact.)
- Is there a scientific side to music?
(Yes, the vibrations made by music are caused by sound waves, whose movements are governed by scientific principles.)
- On your drawings of patterns, what do the areas where the salt has not collected tell you about the movement of sound? What do the areas where salt has collected tell you?
(The areas where salt has not collected indicate that sound waves have moved the salt away. The areas where the salt has collected are areas between waves. These areas are called nodes.)
The Science Teaching Collection: Acoustics site from the National Museum of American History has many other examples of instruments from long ago that illustrate scientific principles. Give students time in class to peruse the site and pick out videos that they like. Students can then share them with the rest of the class.
To learn more about another property of sound—loudness—have students check out the Interactive Sound Ruler.