Demonstrating how to Conduct Controlled Investigations: Example Using Sound
Grade level(s):Elementary School (K-5), Grade 3, Grade 4, Grade 5
Subjects(s):FOSS-Related, Physical Science, Science Skills
When you do a scientific investigation, make sure you are only asking one question at a time. This means that you have to keep everything the same except for one variable you are interested in.
investigation, variable, pitch, volume
What you need:
1 mallet, 1 pencil, 1 foam piece, 2 different sized xylophone tubes
Materials are contained in FOSS Physics of Sound Kit. The xylophone tubes/foam piece can be substituted with two glasses of the same size with different volumes of liquid.
The teacher conducts an investigation to compare the sound produced by two different sized pipes (higher pitch, lower pitch, louder, softer). The teacher conducts the experiment multiple times, each time changing different variables. The students are "directors" and are asked to "cut" the scene when they observe something wrong with the experiment.
Students should understand that scientists ask questions and conduct investigations to answer these questions.
Students should be familiar with the definition of volume and the differences in it. Volume is the loudness or softness (quietness) of a sound.
Students should also be familiar with the definiton of pitch. Pitch refers to the highness or lowness of a sound, Pitch is a subjective sensation in which a listener assigns perceived tones to relative positions on a musical scale based primarily on the frequency of vibration. For some students this will be harder to perceive than for others. Ideally, students should have been given the chance to create higher and lower pitched sounds, in a previous lesson or activity to become familiar with these sounds.
Students will understand the importance of conducting proper investigations. Students will know that an investigation should test one variable at a time. Students will also be able to identify when there are multiple variables changing in an investigation and how to modify the investigation so that there is only one variable.
A variable is anything you can change that might affect the outcome of an experiment. There are potentially many variables that could affect the sound of a pipe, for example: the length of the pipe, the material the pipe is made of, what the pipe is sitting on when being struck, what the pipe is struck with, how hard the pipe is struck etc. The important part of looking at variables is to only change or "test" one variable at a time, if multiple variables are changing then the investigator cannot know which variable is cause the resulting sound etc.
A sound can be characterized by the following three quantities:
Pitch is the frequency of a sound as perceived by human ear. A high frequency gives rise to a high pitch note and a low frequency produces a low pitch note.
"Quality" or "timbre" describes characteristics of sound which allow the ear to distinguish sounds which have the same pitch and loudness. Timbre is a general term for the distinguishable characteristics of a tone. A pure tone is the sound of only one frequency, such as that given by a tuning fork. The basic note has the greatest amplitude and is heard predominantly because it has a larger intensity. Other frequencies are called overtones or harmonics and they determine the quality of the sound.
Loudness is a physiological sensation. It depends mainly on sound pressure but also on the spectrum of the harmonics and the physical duration.
Lesson Implementation / Outline
Tell the students that you would like to conduct an investigation and you would like them to help you conduct it correctly. The question you are investigating is "How does the length of a xylophone tube affect the sound it produces?". Show students the two lengths of the xylophone pipes. You want to see if having different lengths of xylophone tubes changes the pitch or volume, and how the pitch or volume may change.
Tell the students that you will conduct the experiment and if they see that you are doing something improperly, they should say "cut" and use their arms to mimic the board that is used by film directors to indicate cutting a scene.
First do one example where you help them understand what problems they should be looking for. Use the mallet to hit the tube and a pencil to hit the other tube. Note the difference in sound that you observe. Ask the students if you've done the experiment properly (meaning, can you tell if the different lengths of the tubes is what is affecting the sounds they produce or not, when you hit the two tubes with two different objects (one being the mallet and one the pencil)?).
If there are students that recognize the problem, ask them to explain why it is a problem. If none of the students notice a problem, ask them whether they think think that using different mallets affects the sound. Then ask them whether the difference you observed in the sound is from the different mallets or because of the different tubes.
Repeat the experiment, changing different additional variables.
For each additional repetition of the experiment, you can say summarize the previous finding and say "let's try the investigation again. When the students say "cut," call on different students to explain what they found wrong and why they shouldn't do that when they conduct their own investigations. It is possible that students will observe different problems with the investigation, so ask the students whether they have additional comments that are different from what other students have observed.
Additional variables to change (these things students often change unknowingly while they do their own investigations):
- Pick one tube up in your hands to hit it with the mallet and leave the other tube on the foam when you hit it.
- Hit one tube with a lot of force and the other tube with very little force.
- Put one tube on the table when you hit it and leave the other tube on the foam when you hit it.
- Hit one tube with one end of the mallet and hit the other tube with the other end of your mallet.
- Hit one tube with your right hand and the other tube with your left hand.
- Hit one tube yourself and ask another student to hit the other tube.
- Place one tube on the foam by itself and hit it. Place the other tube on the foam without removing the other tube and hit the second tube.
The students should improve their understanding with each additional repetition of the experiment. They also have multiple chances to observe problems because the experiment will be repeated several times. You can assess this by asking different students what they observed that was wrong with the experiment, how it would effect your observations, and how to improve the experiment to eliminate the problem.
Explain to the students that it is very important to keep everything in your experiment the same except for the thing you are interested in and this is true for any type of investigation you are doing in science. Also, explain that sometimes it is easy to do a little thing differently and it can affect the results of the experiment, so they should think carefully about how they are designing and doing their experiment.
Extensions and Reflections
If a human conducts an experiment like the one in this activity, we will be limited in how much we can control the movements of our hand. Even if we try to hit the two tubes in the same way, we are likely to not be able to do that perfectly. Ask the students to think of ways to make sure that the tubes are hit with the same amount of force. Ask them to draw a picture of their idea.
This lesson can also be done for other simple and quick experiments or for measuring. With measuring, the teacher can purposely measure things inaccurately. For example, tilt a graduated cylinder when measuring volume, spill some of the substance that you are trying to measure, read the numbers incorrectly.