TE Activity: Making a Liquid Xylophone
Contributed by: Electrical and Computer Engineering Department, Drexel University GK-12 Program
Summary |
Engineering Connection |
| Acoustical engineers use their understanding of the physics of sound and material properties to create products that sound good or reduce unwanted noise. Projects may range in scope from determining the ideal concert hall shape to produce high-quality sound, to improving on or creating new musical instruments. Acoustical engineers may have designed some of the classroom and school products that improve how well students can hear the teacher. Some acoustical engineers design technologies that use sound beyond the range of human hearing, such as ultrasound technology for medical imaging or sonar technology that enables boats and submarines to detect underwater objects. |
Contents
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| Grade Level: 8 (7-9) | Group Size: 3 |
| Time Required: 90 minutes |
Activity Dependency  :None |
Expendable Cost Per Group
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US$ .50 |
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| Keywords: acoustics, amplitude, beaker, density, ear, frequency, hear, hearing, ketchup, maple syrup, musical instrument, liquid, music, pitch, sound, thickness, vegetable oil, water, xylophone | |
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Related Curriculum
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| subject areas | Physical Science |
Learning Objectives (Return to Contents)
After this activity, students should be able to:
- Explain the general relationship between density and sound.
- Design a musical instrument using beakers and liquid.
Materials List (Return to Contents)
Each group needs:
- 4 - 250 ml beakers of equal height
- 50 ml of water
- 50 ml of maple syrup
- 50 ml of ketchup
- 50 ml of vegetable oil
- Glass stirrer or pen/pencil
- Density and Pitch Worksheet, one per person
For the entire class to share:
- Jug of water
- Bottles of maple syrup, ketchup and vegetable oil
Introduction/Motivation (Return to Contents)
How many of you have ever played a xylophone? How does it work? (Answer: Each long narrow strip of metal or wood is a key. Depending on how long the pieces are, they create sounds that are high or low in pitch.) How do you think engineers knew how long to make the keys? As a critical part of the design process, these engineers would have researched the physics of sound and investigated how metal or wooden pieces create different sounds.
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Today, you will be the engineers designing new instruments. Instead of tapping on xylophone keys, we will be tapping beakers filled with different liquids. To get different notes, we cannot change the size of the beakers. Instead, we will get different notes by changing the type of liquid we put in the beakers! How is the liquid in the beaker related to the pitch it will make? We'll soon find out!
Vocabulary/Definitions (Return to Contents)
| Amplitude: | The height of the wave. The greater the amplitude, the louder the sound. |
| Antinode: | The region of maximum amplitude (crest) between two adjacent nodes in a standing wave. |
| Density: | The mass per unit volume. |
| Frequency: | The number of times the wave oscillates (wiggles) in one second. The greater the frequency, the greater the pitch of the sound. |
| Fundamental frequency: | The lowest frequency produced in a harmonic series, often used in music. |
| Pitch: | How high or low the sound is. |
Procedure (Return to Contents)
Background
Students may wonder why the pitch changes with different liquids. The explanation requires a bit of physics background. A closed tube produces a series of harmonic frequencies when an excitation source occurs at the closed end. The frequencies heard are based on the physical dimensions of the tube and the medium through which the sound travels. The first frequency in the harmonic series is called the fundamental frequency or pitch. These frequencies are heard because they resonate, which means that the waves have an antinode (wave crest) at the open end of the tube. The antinodes of these frequencies occur at one-fourth the wavelength.
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We can calculate the wavelength (λ) of the sound produced as four times the length of tube. click for copyright |
Therefore, we can calculate the wavelength of the sound produced using the formula: wavelength = 4 × length of tube.
The frequency of the sound can be found using the equation frequency = speed of sound ÷ wavelength,
where the speed of sound in air is 343 meters per second, and the wavelength is the value found in the first equation. In this experiment, the wavelength of sound is constant. Since the frequency of the sound changes with each liquid, this must mean that the speed of the sound has changed.
In general, sound travels more quickly through materials that are denser. This is because sound waves are simply vibrations, and it is easier to transmit these vibrations through dense objects, which have more tightly-packed molecules. The four test liquids rank from least dense to most dense in the following order (with general density estimates in parentheses): vegetable oil (0.894 g/ml), water (1 g/ml), maple syrup (1.32 g/ml) and ketchup (1.4 g/ml).
Before the Activity
- Gather materials and make copies of the Density and Pitch Worksheet, one per student.
- Prepare each set of four beakers for each group with liquid substances already poured into the beakers.
- Test each set of beakers to make sure they produce the desired results. Ranked from highest to lowest pitch, the four substances are vegetable oil, water, maple syrup and ketchup.
With the Students
- Using one set of beakers, demonstrate the correct method for making sound from each beaker, which is tapping on each beaker at the same position (towards the bottom).
- Divide the class into groups of three students each.
- Distribute the materials to each group, being careful not to get the liquid substances on the walls of the beakers because this affects the results.
- Hand out the worksheets and have students write down an investigation question, such as: "How does the type of liquid in the beaker affect the sound (pitch) that the beaker makes when I strike it?" Talk with each team about its investigation question and how it relates to the design problem.
- Have students follow the procedure on the worksheet. Remind them that after they have ordered the beakers from highest to lowest pitch and recorded their observations, they must check in with the teacher to get permission to proceed. Check to see that they have correctly completed the previous worksheet steps before proceeding.
- Next, have teams pour the substances together, in any order, into one beaker. Wait 30 minutes or longer for the substances to settle.
- While waiting, direct student teams to work on their poster for a musical instrument design (a post-activity assessment described in the Assessment section).
- Write the orderings of the substances observed by each group, in regards to the pitch, on the board and discuss the results as a class.
- Also while waiting, have students clean the beakers and complete their worksheets up to the density graph section.
- Once the substances have settled, have the students record their observations and finish up the density graph description on their worksheets.
- Conclude by leading a post-activity class discussion as described in the Assessment section. Analyze everyone's final results by comparing them to their original investigation questions and the design problem. Compare density chart drawings. Explore why real results might be different from ideal results.
Attachments (Return to Contents)
Safety Issues (Return to Contents)
- Alert students to be careful not to break the glass beakers and stirrers.
Troubleshooting Tips (Return to Contents)
While the different liquids produce different pitches, some are similar in pitch due to the small contrast in density. Thus, it is critical to take care with following set-up variables before performing the experiment, as they can affect the differentiation of pitches for different beakers containing the same substance: height of the beakers, accuracy of measuring the correct amount of each substance, deformities in the beakers, and/or having substances on the sides of the beakers. The primary factor of concern is the height of the beakers; they all MUST be exactly the same height. Before students arrive in class, tap each set of four beakers to make sure each produces the correct relative high-to-low pitch results.
Investigating Questions (Return to Contents)
- What other liquid substances, besides the ones used, might have a higher pitch?
- What other liquid substances, besides the ones used, might have a lower pitch?
- Is it possible to use a beaker of water and beaker of maple syrup and get the same pitch from both of them by varying the amounts of the substances? Why or why not?
Assessment (Return to Contents)
Pre-Activity Assessment
Discussion/Brainstorming: As a class, have students engage in open discussion. Solicit, integrate and summarize student responses. Remind students that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. This is one way that engineers come up with amazing ideas. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Have them raise their hands to respond. Record their ideas on the board. Ask the students:
- How might you create a musical instrument using various liquids, such as the ones we have here today (ketchup, maple syrup, water and vegetable oil)?
- How would you define density?
Investigation Question: On the worksheet, have students write down an investigation question that will help them with their design problem. (In general, we're investigating the relationship between the pitch produced from a substance and the density of the substance.)
Activity Embedded Assessment
Worksheet: Have students fill out the worksheet as they proceed with the activity. Review their answers to gauge their understanding of the subject.
Post-Activity Assessment
Poster: Have each team create a poster that illustrates and describes their design for a musical instrument. The instrument should in some way use what they have learned in today's investigation, but it can also include additional features.
Analysis/Discussion: After the liquids have finished settling, have students finish the worksheet and compare their final results to their investigation question. Have each group share their results by drawing their density charts on the board. Tell the students what the true results should have been and discuss factors that could cause inaccuracies in the observations (such as beaker imperfections, inaccuracies in the amount of substance in each beaker, students focusing on the amplitude or loudness rather than pitch, etc.).
Activity Extensions (Return to Contents)
For homework, extra credit or during free time, have students experiment with other liquid substances.
Have a set of solids that students can experiment with to see if they find the same relationship between density and pitch.
Have students build the instruments they designed as part of their musical instrument posters.
Have students explore some of the tools that real acoustics engineers use and brainstorm possible scenarios in which they could use these instruments. To start, browse the Acoustics Engineering website: http://www.acoustics-engineering.com/
Activity Scaling (Return to Contents)
- For lower grades, reduce the intensity of explanation to more general concepts without mathematical detail.
- For upper grades, increase the complexity of detail by introducing or having students determine the exact mathematical formulas used to calculate the speed of sound in different types of matter (solid, liquid, gas).
Contributors
Travis M. DollCopyright
© 2008 by Drexel University GK-12 Program. Drexel University GK-12 program, Engineering as a Contextual Vehicle for Science and Mathematics Education, supported in part by National Science Foundation Award No. DGE-0538476.Supporting Program (Return to Contents)
Electrical and Computer Engineering Department, Drexel University GK-12 ProgramLast Modified: May 12, 2010