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Waves and Vibrations Activities. Dale Ingram Education and Outreach Coordinator LIGO Hanford Observatory, Tri-Cities, WA email@example.com 509-372-8248. LIGO: Laser Interferometer Gravitational-wave Observatory.
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Waves and Vibrations Activities • Dale Ingram • Education and Outreach Coordinator • LIGO Hanford Observatory, Tri-Cities, WA • firstname.lastname@example.org • 509-372-8248 LIGO-G1200080-v1
LIGO: Laser Interferometer Gravitational-wave Observatory • LIGO seeks to make direct detections of gravitational waves from astrophysical sources using detectors in WA and LA. • In K-12 outreach, LIGO leverages the excitement of its astrophysics mission to engage students and teachers in inquiry-driven science experiences.
Backdrop . . . • Wave behavior cuts a wide swath through the breadth of LIGO’s research. • WA State Science Standards hold students and teachers accountable for learning outcomes related to waves. • Many southeast WA teachers have told LIGO Hanford that they lack a good personal understanding of waves and they lack good support for waves instruction from curricular materials.
LIGO Middle School Wave Unit -- Find a Copy at www.ligo-wa.caltech.edu/~dale.ingram/wave_unit/ • A 36-page detailed teacher’s guide that contains student handouts. • Support for two sets of station-based wave activities. The first group of activities addresses wave behavior in general. The second set addresses sound specifically. • The big idea: The unit gives kids a chance to explore a number of wave experiments and phenomena as part of a single unit. The activities mix low-tech and high-tech setups. The common thread of wave properties – wavelength, period, wave speed, frequency, amplitude – ties all of the setups together, with contributions from guided instruction and video support (Bill Nye). • The unit is designed to mesh with a field trip to LIGO Hanford Observatory if participating teachers are located nearby.
The Activities . . . General Wave Behavior . . . Waves on a Rope (the lowest of low-tech)
Slinky; Transverse Waves Teachers should look for the long skinny flexible spring shown in the photo below. These are great for transverse waves.
Slinky, Compression Waves Conventional Slinkies are good for demonstrating longitudinal waves as well as transverse.
Waves in a 10’ rain gutter Food coloring makes the water easier to see. Make a plunger that can produce waves without pushing forward on the water. Then drop a few corks in the water to show that the water doesn’t move forward along with the wave. This setup is good for wave speed also. Change the depth of the water and measure the change in wave speed.
Waves on Pencils You can see from the photos how we made these cheap knock-offs of more expensive wave machines that you can find in catalogues. The easiest way to make these is to use two parallel strips of masking tape to secure the pencils. We wanted something more durable, so we drilled a pair of tiny holes in each pencil and wove fishing line through the holes to make the run of pencils. Note that the pencils are oriented in opposite directions along the line to balance their weight. Push the pencil at the end down on one side and release to send the twisting wave through the apparatus. Good for illustrating reflection. Good for illustrating that waves through matter are obtained by the coupling of a number of individual oscillators. The photos don’t do justice to the quality of action that’s available on these units.
Ripple Tank A top-down view. These are standard issue in high school physics labs. A bit spendy, depending on the vendor that you use. The wave maker motor is on the right side of the tank. The red wire runs to it. The black box at the bottom with the white labels is an additional controller that we made to slow down the motor to make it easier to see the waves on the white surface below.
(PHET) Wave Behavior Applet http://phet.colorado.edu/en/simulation/wave-interference
PHET Applets The PHET applets are among the best on the Web for physics concepts, we think. We use these applets to reinforce concepts and behavior that the students will observe in their hands-on experiences. Once students tinker with the ripple tank, for instance, the PHET wave applet becomes something more than just an animation.
Sound Activities What follows are some of the activities in the sound wave portion of LIGO’s wave instructional unit – “phase two” of the unit, during which students reinforce their understandings of wave properties in the specific context of sound.
Vibrations from a Ruler Simple, but its familiar and it reinforces the notion that sound waves originate from something that’s vibrating.
Tin Can Telephones I’ve had bad luck with string phones. After years of R&D, I found that magnet wire works better than string and is a bit more durable. Drill the tiniest diameter hole in the bottoms of the cans. Run the magnet wire through from the outside in, and solder the wire inside the can. Like string, it can/will break if the kids aren’t careful. The sound quality we’ve obtained is about as good as the Taco Bell drive-through.
Falling Dominoes Simulate the Collisions of Air Molecules I’m not crazy about this one because of the absence of oscillations, but our teacher partner likes it because it communicates the idea of the wave passing through the medium – the medium doesn’t move along with the wave.
Tuning Forks Indispensable tools for illustrating the connections between vibrations and sound waves. Also very helpful for developing the concept of frequency.
PHET Applet on Sound http://phet.colorado.edu/en/simulation/sound LIGO-G1200080-v1
Laser Light on a Vibrating Balloon See next slide for comments. LIGO-G1200080-v1
Laser Light on a Vibrating Balloon Procure a section of 8” irrigation PVC. Sand off any roughness on the ends of the tube. The yellow material in the photos is duct tape, which holds the red balloon onto the tube end. We purchased a 36” balloon at the party store and cut off the neck to make a membrane that will fit over the end of the tube (ignore the small hole in the balloon near the edge – oops). Break a little mirror and tape a small piece of the mirror onto the center of the outward-facing side of the balloon membrane. The small can has a laser pointer on top. Point the laser at the mirror so that the reflected light will show up on a marker board or other viewing screen some distance away from the tube (this would be to the right in the bottom photo). Now place a speaker in the opposite end of the tube and play a note through the speaker. We’re using a signal generator to make the note. When you find one of the resonant frequencies of the membrane, the vibrations of the mirror will be captured by the laser light and will show up on the viewing screen as circles, ellipses, figure 8’s and other shapes. We’ve generated some huge and very cool patterns on the viewing screen using the wide tube. You’ll need speakers that give you decent fidelity at low frequencies.
Visible Speaker Vibrations See next slide for comments.
Visible Speaker Vibrations The box on the right is a cheap signal generator. The middle box is a Radio Shack amplifier. On a speaker this big, tones that lie below the low end of human hearing (such as 3 or 4 Hz) produce vibrations of the speaker cone that can be tracked with the eye. We also cut lots of drinking straws into thin strips and tape the strips to the edge of the speaker cone so that they radiate outwards like petals on a flower. When the speaker vibrates, the strips flop up and down and visually amplify the motion of the speaker cone. This system looks very cool if you find a natural frequency for the strips. The flopping motion becomes very exaggerated. This is great for reinforcing the relationship between vibrations and sound waves, and for reminding students that the ear has a limited range of frequency response.
PC with Visual Analyzer Freeware: http://www.sillanumsoft.org/ Visual Analyzer is a superb tool for hands-on wave instruction. We use it all the time. Download and install the software, and you’ll see a default screen that contains an oscilloscope trace (time on X axis) and a power spectrum (frequency on X axis). You might need to adjust the default settings to obtain ranges on the axes that are useful. Email Dale with questions. Most laptops contain built-in microphones, but we prefer using an external mic that’s obvious to the students (We find PC mics at Target stores). IMPORTANT – Visual Analyzer also acts as a signal generator, a capability that really comes in handy if you don’t have a stand-alone signal generator.
Sound Waves in Resonant Air Columns No beer bottles please . Our preference is orange crème soda. The hair dryer is an ultra-quiet model, but it’s still a bit noisy. Our default device is an air pump that’s driven by a bellows.
Bonus Items The following setups are not part of the wave instructional unit, but are used commonly in LIGO outreach.
Sound Wave Matching Our implementation requires a signal generator, an oscilloscope, a microphone, a mixer board, and the necessary cables – items that you might not have in your supply closet. Sometimes, however, these items turn up at garage sales or in the dusty back rooms of schools, or could be donated by a university or research lab, etc. etc. We generate a 300 Hz tone with the signal generator. We split this signal and send it directly to the scope and into the mixer, where we mix it with the channel that’s connected to the microphone. The mixed output goes to the other channel of the scope. Students grab the microphone, and if they can match the pitch of the 300 Hz note (we also use a speaker to play the note), they’ll see that their humming on the mixed channel matches the waveform of the sound waves that come from the signal generator. Students of all ages love this one.
Resonant Sound Tube The laptop is running Visual Analyzer, which we’re using in the wave-generator mode. The software is making a ~250 Hz note that’s playing into the acrylic tube. When the sound travels from the speaker down the tube, it reflects off the rear wall of a soup can. We removed the lid from the can but left the can bottom intact, other than to drill a small hole in it and poke a string through the hole into the inside, then knot the string on the inside. This allows the can to be pulled through the tube in the direction that’s opposite the speaker. When the position of the can allows the sound waves to resonate in the tube because the length of the air column is correct, then the sound of the tone becomes distinctly louder. This activity provides a good exposure to resonance and constructive interference.
Model Interferometer The photo shows a top-down view. Find this model and other LIGO-related activities and information at http://www.einsteinsmessengers.org/ Demonstrate the constructive and destructive interference of light in an interferometer by using this model made from wood and string. The particular design of this model allows users to visualize the effect of gravitational waves on LIGO’s interferometers by moving the end mirrors in the model (the wood blocks) back and forth in an alternating way.
Michelson Interferometer The interferometers on the previous two slides are made of fancy parts that we had on hand in our labs at the observatory. You can build the same design from non-fancy parts and obtain an interferometer that works nearly as effectively. LIGO offers one recipe here: http://www.ligo-wa.caltech.edu/teachers_corner/lessons/interferometer_9t12.pdf and another one here: https://dcc.ligo.org/LIGO-T0900393-v1 Interferometers are great tools for illustrating the constructive and destructive interference of light and for introducing your students to precision measurement techniques.
Matched Filtering Activity LIGO-G1200080-v1
Matched Filtering Activity This is another activity that’s available via http://www.einsteinsmessengers.org/ Students experience a model of how LIGO analyzes detector data to search for gravitational wave signals from neutron star pulsars. It’s a good application of basic wave properties – amplitude, frequency, the behavior of periodic systems. It’s also a nice introduction to instrumental concepts such as signal-to-noise ratio.
Acknowledgement • Support for LIGO comes from the National Science Foundation. • NSF also funds the Research Experiences for Teachers program under which Keith Plewman served at LHO.