Harness your students' passion for music
to motivate them to learn the physics of sound with PASCO's new Sonometer.
[Resonance Modes in a Vibrating String]
Any student that has played a string instrument, like a guitar or violin,
knows that changing the tension in the string changes the sound.
The PASCO Sonometer allows them to find the mathematical relationship between tension and frequency
by enabling the accurate measurement of each quantity.
Students start by hanging a 0.5 kilogram mass on the tensioning lever.
They level it using the tuning peg and a built-in bubble level.
This ensures an accurate value for the tension.
The tension is five times the weight because the mass is five times further from the pivot than the string.
Students set the wavelength by sliding the bridge
until the indicator is at the desired position on the built-in ruler, in this case, 0.45 meters.
The string is fixed at both ends, so the wavelength is twice the string length, or 0.9 meters.
Students pluck the string and measure the frequency using a PASCO sound sensor
and the FFT display in SPARKvue or PASCO Capstone software.
Let's take a measurement here.
I'm going to hit Monitor. It's picking up my voice now, so I'll be quiet.
We can quickly measure the frequency with the coordinate tool: 377 hertz.
Students would then add 0.5 kilograms to the mass hanger, level the tensioning lever again,
and repeat the frequency measurement.
Once they have five or six data points, they use the tools in SPARKvue or PASCO Capstone software
to find the relationship between tension and frequency.
They find that a graph of tension versus frequency squared is linear.
They extend their analysis to find the relationship between tension, wavelength, and wave speed.
They predict the linear mass density of the string and check it
by calculating the linear mass density using the diameter of the string, or the gauge, and the density of steel.
They also can calculate it from the mass and length of the spare piece of guitar string.
Students assess their understanding by predicting the frequency of the string
at a new wavelength and then testing it with a measurement.
There's an alternative approach that uses tuning forks instead of the sound sensor.
The frequency is fixed instead of the wavelength.
Students find the length of string that resonates with the tuning fork frequency for each tension.
The paper riders make that resonance visible.
A paper rider is a little piece of paper bent into a V shape.
I like to put a few on for dramatic effect.
Sometimes one will move a little bit more than others.
We have the tuning fork.
I strike the tuning fork and then slide the bridge until I see resonance.
I saw a little bit of motion there. Let's confirm it.
I had it right. They all jumped off.
They discover that a graph of tension versus wavelength squared is linear.
After further analysis, they learn the relationship between tension, frequency, and wave speed.
They assess their understanding by predicting the length of the string
that will resonate at a different tuning fork frequency.
Both methods offer students an engaging and reliable way
to experimentally develop relationships that are important in physics and the world of music.
You'll find detailed lab instructions and a teacher guide for this lab, and more, in the PASCO Experiment Library.
Look for more Sonometer videos on the PASCO Sonometer web page or our YouTube channel.
Thanks for watching and listening.