Lesson 4

Pressure Waves and Human Hearing

Safety

Loud noises can damage ears and hearing permanently.

No yelling is permitted by students at any point today. Students should make quiet noises only.

Website resources for Safety and Health for Human Hearing (use only if you want more information):

Educational Standards:

NGSS

4-PS4-1. Develop a model of waves to describe patterns in terms of amplitude and wavelength and that waves can cause objects to move.
4-PS3-2. Make observations to provide evidence that energy can be transferred from place to place by sound, light, heat, and electric currents.

How Humans Make and Hear Sound

Humming

Teacher Notes: Students should hum softly and not press hard into their neck.

If students are struggling to change pitch, ask them to try to hum "eeeeeeeeee" (this usually comes out as a higher pitch) and "uuuuuuuuuuuu" (this usually sounds like a lower pitch).

Student Directions

Use your fingers to gently feel where your hum begins and travels. What does it feel like?
Hum louder and softer. How does that change the feeling of the hum?
Hum with higher and lower pitches. How does that change the feeling of the hum?
How do we hear a hum?

Sound Simulations

www.physicsclassroom.com/Physics-Interactives/Waves-and-Sound/Simple-Wave-Simulator/Simple-Wave-Simulator-Interactive

https://www.acs.psu.edu/drussell/demos/waves/wavemotion.html

Tuning Fork and Sound Wave - JavaLabTuning fork The tuning fork has a structure that combines the ends of two sticks. When the tuning fork is...

The simulation on the left works well to show the energy dissipation over distance away from the source. It is also easiest to see when you turn off the basic motion of air molecules and increase the frequency.

https://javalab.org/en/tuning_fork_and_sound_wave_en/

Drum Vibrations

Materials

1 Drum per student

1 disposable cup (either paper or plastic is fine)
1 rubberband
1 plastic wrap
salt (a pinch)

Per table

a tuning fork and mallet to be shared

Instructions

Create the drum by placing a piece of plastic wrap over the top of the cup.
Use the rubberband to pull and keep the plastic wrap snug over the top.
Sprinkle the pinch of salt on top of the plastic wrap so that it is evenly spread.
Holding the tuning fork away from the cup, strike the tuning fork with the soft side of the mallet. It should not be loud.
Bring the vibrating tuning fork close to the top of the drum. DO NOT TOUCH THE TUNING FORK TO THE PLASTIC WRAP!
Students should observe the movement of the salt.

PXL_20230501_224724161.TS.mp4

PXL_20230501_224902214.TS.mp4

PXL_20230501_224954812.TS.mp4

Human Hearing Videos

Video Summaries: Sound waves (pressure waves) are funneled into the ear and reach the eardrum, a membrane sensitive to the pressure differences. The eardrum vibrates from the pressure of the sound waves similar to how the tuning fork caused the plastic wrap and salt vibrate yesterday. The eardrum vibrations move the three tiniest bones in the human body - the middle ear bones. From there, the vibrations travel to the cochlea (pronounced "Coke-lee-uh") which is attached to the auditory nerve that sends the signal to the brain. The brain processes the sound for frequency and intensity of the sound waves. With frequency and intensity and two ears on either side of the body, the brain makes pretty good guesses for location of sound sources and motion of the sound source.

Feel free to show your favorite videos on hearing. If you have one you prefer that isn't on here, please let us know in the class feedback for the week.

Human Hearing Frequency Ranges

Use the website https://www.szynalski.com/tone-generator/ to test student hearing. Make sure the sound is not too loud or uncomfortable for students or yourself.

You can press the PLAY button or use the space bar to play the sound from the website. You can use the slider or the arrow keys to change the frequency.

Start at frequency of 1 Hz and use the arrow keys on the computer keyboard to gradually increase the frequency to 20,204 Hz. If you use the computer arrow keys, this will take just under 4 minutes. You can also drag the slider for a faster test. Using the arrow buttons on the website will take the longest. Feel free to play around with the controls.

Lab: String Telephones

Goal: Students should see how vibrations make sound and sound makes objects vibrate.

Students work in pairs to build their string and cup phones, design their investigations, and report their findings to the class for feedback on procedure and predictions.

Review safety with students: Students should make quiet noises. If their cup gets crumpled, it will stay crumpled.

If some groups want to work together, that is up to teacher discretion.

Lab Materials per pair

Each pair of students will need:

2 disposable cups
string (3 to 5 meters in length)
1 pushpin
2 paperclips

Build Phones

Use the pushpin to make a hole in the center of the bottom of each cup. If the teacher is comfortable, students can do this, otherwise, the teacher can poke holes in each cup prior to passing them out to students.

PXL_20230502_155326041.TS.mp4

2. Place the end of the string over the hole. Use the pushpin or use a paperclip to push the string through the hole.

PXL_20230502_160623854.TS.mp4

3. Pull the end of the string through the inside of the cup. Tie a paperclip to the end so that the string won't get pulled back through the hole.

String Guitar

Have students work together for this one and take turns.

Have students pluck the string so that the sound is not transferred to the cup. You can do this with extra string or just by holding the string as seen in the video on the right so that the string is slack against the cup.

Next hold the the string taut against the cup and pluck the string again. Allow students to experiment with changing the distance (wavelength) and amplitude of the pluck.

Have students also try just running their fingers along the string and experiment with the tension in the string as they do so.

PXL_20230503_004930205.TS.mp4

Telephones

Prediction and Testing

Make sure students make a prediction prior to testing the cups. Students should not yell into cups.

Taut String

Loose String

Observations

Students should notice how the cup and taut string will amplify and distort the sound being transmitted.

Analysis, ImprovemEnts, and Discussion

Go over the discussion questions in the lab handout.

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