Physics of Sound
BASEE workshop
CONCEPTS:
· Sound is energy
· A Sound System (force, vibration, medium, receiver)
· Properties of materials affect the sound you hear
· Pitch ~= rate of vibration = frequency
· Resonance (when the force is synchronized with the natural frequency, making the volume or amplitude of the vibration stronger)
· Where the force is applied affects the sound
· Waves and modes of vibration (harmonics)
· Math (simple)
· Sounds are complex
SKILLS:
· listening for subtle differences in sound
· describing sound (scientifically and qualitatively)
· asking questions
· developing experiments
· graphing
PEDAGOGY STRATEGY:
· provide lots of time to "fool around with stuff"
· give them a challenge to explore
· refer to the Sound System and frequently ask: what's vibrating? What's the force?
· Provide journaling time (how does this work? 15 minutes of quiet?)
· Every day start with some music and end with some music
· Every day ask "What do you know (or did you learn)? What would you LIKE to know?"
Equipment and Supplies
Introduction
q Slide set
q Cocoa powder
q Mug and metal spoon
q Hot water
Exploration: How Sound Travels (measure the speed of sound)
q photo flash mounted on flourescent poster board
q clip leads
q tripod
q pair of marching cymbals
q two flags
q 6 stopwatches
q poster board (qty 4, for histogram)
q colored 1" dots (for data)
Exploration: Visualizing Sound
q stroboscope w/tachometer
q Cool Edit software
q Computer w/soundcard
q Microphone (2)
q preamp
q amplifier
q oscilloscope (w/clip leads)
q 12” speaker with grill removed
q keyboard
q guitar
q kettle drum
q white 1" stickers
q water bowl and tuning fork
Exploration: What's Vibrating?
q Stemware (24)
q Glass 2 Liter bottles (8)
q Plastic 2 liter and 1 liter bottles (2 each?)
q Water
q Large rectangular tub (portable sink)
q Oil
q Corn syrup & maple syrup
q Condensed milk; whole milk
q Wooden sticks (spoons? Chop sticks?)
q Plastic rulers
q Metal spoons
Exploration: Sound and Properties
q Pre-Made String telephones:
q Plastic cups
q OJ cans
q Large coffee cans
q String (heavy)
q String (light)
q Wire
q Shaker Fruit
q Cowbell and Different Mallets
q Pringles cans and fillings (in ziplock bags):
q Rice
q Sand
q Beans
q 30gal galvanized garbage can
q carpeting or foam rubber to put inside can
q ear protection headset
q Drum set and other percussion instruments
Exploration: Waves
q slinkies (5+)
q 8 meter sticks
q rope
q marbles
q kinetic energy model
q dominoes
q wave tank w/2x4 on a stick
Exploration: Resonance
q wave form generator
q amplifier
q 10 gallon sparklets bottle
q glass bottles
q 7 basketballs (or red playground balls)
How Ears Work
q ear model
q 60 plastic 2L soda bottles
q saran wrap
q scotch tape
q rubber bands
q toothpicks
q hotglue
q 1/4" rubber tubing
q cardboard lids
q otoscope
q photo of ear
q article handouts w/ WWW and book references
q factors of 10 poster with strings cut to 1,10,100 inches, and a spool of 1000 inches to wrap around the room
q handout re: decibels
Sound Systems Defined
q call bell
Sound System: Strings
q Guitar
q Guitar
q Mandolin
q Banjo
q Violin
q Meter sticks (8)
q Hammered dulcimer
q Premade Bouncy Nuts (bagged in ziplock- 15 sets):
q Rubber bands
q Big nuts
q Small nuts
q CD of Mozart
Sound System: Percussion
q Kettle drum and sticks
q Drum set
q Xylo's and Glockenspiels (6) "Orph"
q Shaker fruit and cowbell
q Tape of STOMP
Sound System: Woodwinds and Horns
q CD of John P Souza
q Twirling tube
q basketball
For each team:
q Flip chart paper
q Colored marking pens
q Straws (30)
q Scissors
q PVC end caps (30) pre-drilled
q PVC 1/2" tubes cut to 4,8,12, 16" (5 sets)
q PVC 1/2" connectors (10)
q PVC end caps (30)
q PVC flute mouthpieces (4" w/.375" hole + connector)
Team 1 and Team 2:
q Oboe
q Clarinet
q Harmonicas (6)
q Harmonica guts
Team 3
q Flute
q Ocarinas (6)
q Nose flutes (6)
Team 4
q Recorder
q Penny whistle (6)
Team 5
q Trombone
q Trumpet
q Slide whistles (6)
Other Stuff:
q CD player
q Overhead projector
q Two classrooms
q VCR
q 15 feet of 3'wide butcher paper
q yellow 8 1/2 x 11 paper
q magazines (to cut out)
q glue sticks
q scissors
q colored (large) felt tip pens
q Folders/notebooks for handouts and journals
q Extension cord
q Power strips
q 2 rooms
q internet access Tues lunch, 3-4 & Friday lunch
q variable speed drill
Exploration Station:
Waves
Key Concepts
· A Wave is a transfer of energy
· The medium doesn't move very much
· Frequency is how fast the energy pulses come at you (cycles per second)
Introductory question:
· Where have you experienced waves?
Ropes
· On the floor, have one person hold the end of the rope, the other person flicks the rope; what's traveling? Is the rope going anywhere? (no)
· What's moving? (the energy)
Dominoes
· Set up a line of dominoes
· Push the first one over and watch the transfer of energy (a wave of sorts); again, the dominoes themselves aren't going very far… but the energy is!
Marbles
· To see how energy is transferred on a molecular level (sort of like air molecules), line up marbles between two parallel yardsticks on the floor; roll one marble into the line and watch energy transfer between the marbles (this is like air molecules bumping into each other)
· Do the people demo: stand everyone in a line shoulder-to-shoulder, with their right hand out; the person on one end slaps the hand next to them, who in turn slaps the next hand (suggestion: after you "pass the slap", return your hand to an outstretched position directly in front of you, sort of like how molecules return to their same average position); launch one wave, then try a series of slaps in a row; launch a wave and have the last "slap" reflect back, launching a wave in the other direction
Slinkies and Speakers (strobe)
· Stretch slinky about 4' apart; hold one end, and apply an impulse;
· Pulse it repeatedly, but slowly, and see the distance between the compressed rings
· Pulse it faster, and see the distance between the compressed rings decrease
· Play a tone through the boombox and lightly touch the speaker with your fingers; feel it vibrate in and out; use the strobe to see it move in and out
· Discuss picture of compression waves (low freq) from speaker; compare slinky and speaker
· Show picture of higher freq compression waves and have them plot the pressure (similar to the low freq drawing, only the peaks are closer together… there are more pulses each second
Summary discussion
· How do waves behave?
· Any surprises? Questions?
Exploration Station:
The Speed of Sound
Key Concepts
· Sound travels slower than light
· Measurements are not precise
Introductory question:
· What evidence do you have that light travels slowly? (echos, thunder and lightening, baseball game crack-of-the-bat from the center field bleachers, starter gun at a race where the smoke can be seen before the gun sound, …)
Demonstrate at Close Range
· Show how the flash is triggered at the same time as the cymbals crash
· Do this up close so everyone can see that they start at the same time (if they miss this, they won't believe their eyes later!)
· Practice using the stopwatches ("start and stop with the right button; clear with the left"). Ask them to start the watch when you say "flash!", and stop the watch when you say "crash!". Try it several times.
· Explain the flags: the "flasher" will drive far away; when he's ready to crash/flash, he will wave the flag; the teachers will wave their flag in response to indicate that they are ready with their stopwatches
· Explain that they'll take turns using the stopwatches; take two measurements then let someone else take the next two measurements (so everyone gets a chance, and so you can pool the data)
1/10 of a mile
· Do 3 crash/flashes with the first 5 teachers, then 3 more with the 5 other teachers
· Make sure everyone writes down their results ("good" and "bad" data)
· Drive to the next spot farther away
2/10 of a mile
· Repeat as above, with a total of 6 crash/flashes
Plot the data
· Create a histogram for each distance (one posterboard for 1/10 mile, another for 2/10 mile)
· Use 0.1 second buckets (columns) for the histogram's x-axis
· Ask the teachers to place a dot in each bucket for each of their data points. If there's a dot in the bucket, place your dot ABOVE that dot (the Y-axis becomes the # of occurences)
· Be sure to create two separate histograms for each distance
Summary discussion
· Why does the graph have the shape that it has? Why isn't all the data in the same bucket? (measurement error)
· What are the possible sources of error (variations in reaction time; accuracy of stopwatches; variation between stopwatches; the cymbal sound is spread out over time CRRRAAAASSSHH)
· Why are the two histograms different? (the reaction time error is the same, but it's proportionally smaller than the total time)
· What's "the answer"? (pick an average, or better yet state the answer in terms of a likely range)
· Extra credit: convert the measurement into miles per hour or meters per second (=approx 1000 ft/sec or 330 m/s… on a warm day at sea level!). This is well beyond the algebra abilities of most K-5 teachers.
· Any surprises? Questions?
Exploration Station:
Seeing Sound
Key Concepts
· The sounds you hear are complex, made of several tones combined
· Instrumentation can help a scientist see and measure very fast events
· Oscilliscopes plot data (y-axis) over time (x-axis)
· A "tone" can have "overtones" that impact the qualities of the sound
Introductory question:
· Sing a note together (LAAAA). Why does each person's voice sound different?
· Break into two groups, spending half the time at each substation
Oscilloscope
· Discuss how the oscilloscope "plots" data as it happens (intensity over time, as it happens)
· Try different sounds and see how the patterns change (quiet vs. loud, hi vs. low pitch, voices vs. triangles vs. bottles, short sounds vs. sustained)
Sound Capture
· Discuss how the computer "captures" the sound and the software plots (intensity over time, but after the fact)
· Have it generate a simple A440 and show the Intensity vs. time plot
· Analyze it, and show that it consists of one frequency component on the Intensity vs. freq plot
· Have them try various sounds, starting with loud vs. quiet and see how the plot changes
· Capture a singing voice ("Laaa") that matches the pitch of a tuning fork or harmonica; analyze a slice in time, looking at the various frequencies that make up the "tone"; do the same for the harmonica
· You will probably need to spend a little time talking about what the graphs mean (refer to the handouts)
Summary discussion
· Any surprises? Questions?
Exploration Station:
Resonance
Key Concepts
· Most objects have a "natural frequency" at which they like to vibrate
· If the force is synchronized with the natural frequency, then the object "resonates" and the vibration gets (suddenly) more intense (louder, stronger)… or, it takes very little energy to keep it vibrating.
Introductory question:
·
Resonating Air
· blow in bottles; what's vibrating? (remind them of the slinky waves, and imagine them bouncing from the top of the bottle to the bottom of the bottle)
· In general, volumes of "space" have a natural frequency at which they resonate. Discuss: have you been in a place that has a bright sound where echoes happen easily? (tiled shower stall, marble hallway of a 1920's building, bathroom…) . Let's experience it ! Put the garbage can over your head and sing! See if you can find the note that makes your singing sound louder (we'll try to measure it later).
· In the case of a column of air like this, it's very difficult to see the force (a little bit of air bleeding over the lip of the bottle) and the object that's resonating (the air)
Resonating Pedulums (or swings)
· imagine the pendulum as a swing; Try pushing the person in the swing… what are you doing to keep them swinging? (pushing at the right time). See what happens when you apply the force to soon or too late
· See what happens when you shorten the string length (the natural frequency increases, so the frequency of the force must increase, too)
Resonating Basketballs
· try dribbling the ball; how do you keep it going?
· What happens when you dribble waist high compared to 6" off the ground?
· How does this compare to the pendulum?
Measuring the Resonant Frequency
· Put the 10 gal. Bottle (filled with a 1/4" of water) on the guitar amp
· Drive the speaker with the wave form generator, trying different frequencies… Watch the water! (find the lowest frequency that makes the system resonate, and you'll see the water dance!)
· Place the garbage can over the speaker and see if you can find its resonant frequency
Structures Vibrate, too (Tacoma-Narrows Bridge clip)
· Resonant frequency of structures is critical to their safety (wind, earthquakes)
Summary discussion
· Any surprises? Questions?
Exploration Station:
What's Vibrating? Goblets and Goo
Key Concepts
· The Touch Test: if you touch it and the sound changes, then it was vibrating
· Adding mass makes a vibrating system slow down (and hence, the pitch drops)
· Some materials absorb sound energy and eliminate vibrations
Introductory question:
· What sound does a goblet make?
Goblets Empty
· Try each of the goblets (empty) and see what sound they make. Are they all the same?
· What's vibrating? Do the Touch Test
Goblets w/ Water
· Predict what will happen to the pitch when you add water to the goblet
· Try it!
· Are they all the same? Why not? (discuss variables such as water level, glass thickness…)
Goblets and Goo
· Can you predict what will happen to the sound using other liquids? Try it! (compare using matched sets of goblets; small differences are hard to hear, so milk vs. oil might be better)
· What is different about milk and oil? What happens when you mix them?
Mass and Vibration
· So, why does the pitch drop when you add liquid? Explore how mass changes a sound system
· Imagine slicing the goblet in half… simplified, it looks like a beam cantilevered out into space; try it with plastic rulers suspended over the edge of the table
· Tape 5 large heavy nuts to the lower half of the ruler; what happens to the vibrations?
Summary discussion
· Any surprises? Questions?
Exploration Station:
Properties of Materials
Key Concepts
· The sounds you hear depend on the properties of all the materials involved
· The sounds also depend on how and where the force is applied
Introductory question:
· Why do sounds sound different?
Pringles Shakers
· Try each of the shakers