Contributed by: Greg Stiles, Cleveland School for the Arts, Cleveland, OH
Science instruction is most effective when using a hands-on delivery system. This lesson will use your students’ natural affinity for music and musical instruments to reinforce and refine their knowledge of the nature of sound - specifically, that sound is produced by vibrations, and that the frequency of the waves produced by these vibrations determine the pitch of the sound.
Upon completion of this lesson, the student will be able to:
- Correlate string tension with sound pitch.
- Describe how string mass (thickness) effects sound pitch.
- Demonstrate an understanding of the physics of the acoustic guitar.
Materials: Per student or team
- One rectangular cigar box (call a tobacco shop if you cannot find enough)
- Four 120cm lengths of nylon fishing line - 4lb. test
- Four 120cm lengths of nylon fishing line, 1 each of 4, 10, 13, and 17 lb. test
- Four push pins or thumbtacks
- One triangular ruler, such as an architect’s rule, or a triangular piece of wood longer than the cigar box’s width
- Four 200g weights
- Four increasingly heavier weights - 100g, 200g, 300g, and 400g are ideal for this lab. If no lab masses are available, lead fishing sinkers of comparable mass will suffice.
- One guitar pick. The plastic tabs which keep bread wrappers closed will work.
Two to three 40 min. periods, depending on the skill level of the students and the amount of discussion generated.
Junior high to high school physics.
- Before beginning this activity, place the following key definitions on the board:
- Frequency - The number of complete waves which pass a given point in one second.
- Amplitude - Half the distance from the crest of a wave to the trough.
- Pitch - The relative highness or lowness of a sound, which is a function of wave frequency in direct proportion.
- Volume - The relative strength (loudness) of a sound, which is a direct function of a wave’s amplitude.
- Review the above definitions as needed, then begin the activity.
- Tie a knot in one end of all of the lengths of line.
- Select the 4lb. test lines. To one of these lines, tie a 100g weight to the end of the line opposite the knotted end. Repeat this procedure with the 200, 300, and 400 gram weights.
- Locate the 4, 10, 13, and 17lb. test lines, and to the ends opposite the knotted ones, tie the four 200g weights.
- On the cigar box, locate one of the narrow ends. Make 4 marks at equal intervals on the top of the box. If you make a mark every 3.5 centimeters, that should suffice.
- Choose the equal thickness/increasing weight lines or strings. Push a pin through the knot opposite the weighted end of each of the strings. Beginning with the 100g weight/string, and continuing with the 200, 300 and 400g strings in that order, push the pins firmly into the first, second, third, and fourth marks.
- Place the box near the edge of a table. Stretch the weighted ends of the strings across the length of the box and down the side of the table so that the weights hang freely, holding the box with one hand so that is does not slide off the table.
- Place the triangular rule under the strings across the width of the box approximately 4-5cm from the pins so that all four strings are supported. The rule should be parallel to the end of the box with the pins.
- Do not remove the rule during this step. Using the pick, strum each string individually approximately 2-3cm from the rule and between the rule and the weighted end.
- Questions to answer:
- How does the sound of each string vary from one to the next? [It gets progressively higher.]
- Which string gives the lowest pitch? [The string with the lightest weight (100g)]
- Which string gives the highest pitch? [The string with the heaviest weights (400g)]
- What variable has caused the differences in pitch between the strings? [The progressive increase of the tension on each string caused by the weight differences.]
- Can you state a correlation between string tension and pitch? [The greater the tension, the higher the pitch.]
- Remove the rule and push pins. Locate the set of equally weighted strings. Remember, these are the strings of differing thicknesses. Beginning with the 17lb. string, and continuing down to the 4 lb. string, insert their pins into the holes as in #5. If the fit of the pins is too loose, make new holes immediately adjacent to the others, as the pins may pull out otherwise. As in step #6, stretch the strings across the box and let the weights hang freely. Replace the rule as in step #7.
- Strum each string individually approximately 2-3cm from the rule and between the rule and the weighted ends, beginning with the thickest string and continuing to the thinnest.
- Questions to answer:
- How does the sound of each string vary from the first through the last? [It gets progressively higher.]
- Which string gives the lowest pitch? [The heaviest or thickest one.]
- Which string gives the highest pitch? [The lightest or thinnest one.]
- Which variable is responsible for the change in pitch? [The change in the thickness of the strings. In music, this is known as the gauge of the string.]
- What is the correlation between string thickness (gauge) and relative pitch? [The thicker the string, the lower the pitch; the thinner the string, the higher the pitch. This is a result of the thicker string having a greater mass, causing vibrations of lower frequency to occur. The converse would be true for the thin, or light string.]
Evaluation may be carried out through standard testing format, although an essay type of question would be more apropos to ascertain a working knowledge of the principles contained in this lesson. This type of lesson would be ideally suited for portfolio assessment, particularly in an arts-based or cross-curricular educational setting, as it would allow for a wide range of evaluation possibilities, which might include the artistic design and construction of a more elaborate and durable guitar. (A source of guitar building supplies follows.) In addition, the student might compose and perform a piece of music which would illustrate the tonal and pitch differences described in this lesson.
King of the Surf Guitar: The Best of Dick Dale & His (Rhino, RNLP 70074)
“Manic Depression” Are You Experienced? (Polydor, 847 243-2)
“Dazed and Confused” (Atlantic, SD 19126-2)
Stewart-MacDonald Guitar Supply Company, 21 North Shafer St., Athens, Ohio,