Extended Investigation of a musical instrument
Sound. Musical instrument analysis (toy or real instrument + Laptop + optional headphones)
Software is required on PC/laptop with microphone and speakers. iPod earphone make an adequate microphone.
There is lots of expensive software but I found the following freeware:
Signal generator and analyser software from http://www.techmind.org/audio/index.html
Downloadable wav files (wave shape, frequency, sweep, log/linear etc) http://www.audiocheck.net/
Hearing response curve (use headphones) http://www.phys.unsw.edu.au/jw/hearing.html
Aim: to investigate the production of sound from a musical instrument.
Method:
Choose a musical instrument
Analyse the sound when a known note is played
Determine the frequency and measure the wavelength
Find the relative level of any harmonics present
Determine the speed of sound in air
Detail:
Play a particular note on the instrument and measure the frequency (use “tuner”)
View the waveform and show how close the sound is to a pure sine wave, or combination of sine waves (overtones).
The spectrum analyser program can help find overtones.
What was the relative intensity or loudness of these harmonics?
Measure the length of the “tube” if a wind instrument, or “string” to determine the wavelength.
Students can find the speed of sound in air for wind instruments. Experimenting with stringed instruments find
the speed of sound in the string that depends on tension etc, so less useful analysis.
Questions:
1. Does the note you are playing match the frequency designated to the note?
2. Were the harmonics that were present as you expected? Show calculations.
3. How can you tell the difference between two instruments if they are playing the same note?
Your report should contain a detailed response to the above questions including your error and possible sources of
error.
Your report needs to include:
What instrument was used.
Partner name.
How you performed each of the measurements including the equipment and/or software used.
All calculations and formulae used.
Marking
Explanation of experiment and how instrument produces sound
(advanced, thorough, sound, basic, unclear)
Explains concepts clearly and accurately
(advanced, thorough, sound, basic, unclear)
Correct physics terminology used
Applies relevant concepts and ideas
Links information and data
Uses algorithms to reach suitable solutions
Makes cause/effect judgements
Awareness of safe practices
(high, medium, low)
PFI
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Sample calculations:
For the “mini plastic recorder”
Playing a “note” G of the 5th octave.(approx. 784 Hz)
Use signal generator to show the frequency is: ____________ Hz
Play both at the same time. Do they sound like they are the same pitch?
Now use the signal analyser (built in fast fourier analysis to go from frequency domain to time domain).
Play your instrument and capture a typical waveform. Use screen capture such as
What is the frequency of the first peak (fundamental)? ____________ Hz
Second peak? ____________ Hz
Third peak? ____________ Hz
Do you think you correctly found the fundamental frequency? Give reasons?
Using the oscilloscope, what features can you see?
Now, measure the effective length of the instrument. Mouthpiece to first open hole. _____ cm, or ______ m
The mouthpiece is considered to be the “closed” end, and the first hole the “open” end.
One wavelength is therefore: ______m
Using the wave equation v=λf
we can calculate the speed of sound in air as: __________ m x __________ s -1 = ____________ ms-1
Find today’s temperature and what the speed of sound in air of this temperature should be. __________ ms -1
Comment on any difference and possible sources of error.
* comment. In general, this experiment yields quite acceptable results. Different instruments show different levels of
harmonics and students could comment on these differences.
Woodwind and brass instruments yield the speed of sound in air, but of course, stringed instruments yield speed of
sound in the string which will depend on string gauge and tension.
When measuring the pipe length, be careful when determining where the open and closed points are.
* links to Structures and Materials, but a demo with Non-Newtonian materials may add interest to Sound
Equipment lamington tray, cornflour (1 Pack), powered speaker
Method
Mix cornflour with water until you have a smooth paste
Place tray on speaker – very loud. 73.5 Hz square wave. If you have an old speaker, line with plastic wrap and pour
cornflour paste straight on. Less volume needed.
May need to poke with finger to start.
* See video
PFI
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Amazing golf shot – projectile motion
Dr Altman YouTube clip (Type one motion)
Watch the clip at:
http://www.youtube.com/watch?v=fKi3xwVikB0&feature=related
or search with “dr altman amazing golf shot maths”
Draw the projectiles path then label the diagram with distance travelled and time information
Calculate the time it takes the ball to reach maximum height?
What is the vertical velocity when the ball is at its maximum height?
If a ball was dropped from the height in the previous question what velocity would it have as it hits the
ground?
Use the last answer to find the initial vertical velocity (magnitude and direction).
What is the horizontal velocity of the golf ball?
Use your answers to calculate the magnitude and angle of the initial velocity.
PFI
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Coanda Effect
Hold the teaspoon so it can swing freely.
Using a straw, blow a stream of air close to the convex curve of the spoon.
Use a diagram to describe was you observe.
You need to know:
The Coandă effect is the tendency of a fluid jet to be attracted to a nearby surface.
Tritton, D.J., Physical Fluid Dynamics, Van Nostrand Reinhold, 1977 (reprinted 1980), Section 22.7, The Coanda Effect.
If the stream of air “sticks” to the spoon, the stream is “bent”. Draw this diagrammatically.
Now, with the mass of the air deflected as you have shown, show the force exerted on the spoon.
Rotate your diagram 90° with the convex curve pointing upwards. Imaging this is a wing.
Using what you now know of the coanda effect, describe how this would help an aeroplane fly.
PFI
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Nuclear history
Nerdling Magazine article – nuclear edition questions
1. What is radiation?
2. What is nuclear radiation?
3. Why are people so scared about radiation?
4. Where is radiation?
5. The picture on page 3 shows people viewing a nuclear bomb!!! Are they at
risk?
6. What is an isotope?
7. On page 8, how is ionising radiation defined?
8. Why is radiation dangerous to living things?
Marie Curie died for her science
9. What radioactive products were available in the 1920s and 1930s?
Care to purchase some “irradiated water”?
10. Cities or suburbs often say they are “nuclear free” – can this be true? Why? Why not?
11. Calculate your daily radiation dose on page 17.
12. What was the point of the radiation treasure hunt?
13. How much for a lump of radioactive uranium?
14. What was the difference between ‘Little Boy’ and ‘Fat Man’?
15. When was the first nuclear explosion?
16. At the Nevada Nuclear Bomb test site – could you really wipe off the radiation?
17. What is the fence on page 29 used for?
18. Where in Australia was the biggest bomb detonated. How many radioactive bomb sites are there?
19. Who set off the bombs in Australia?
20. What was found out in 2001 about some of the bomb testing in Australia?
21. Which country has done the most nuclear testing?
22. How many deaths are attributed to nuclear bomb testing?
23. How many people did the Nagasaki bomb kill?
24. Name you favourite atomic super hero.
PFI
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Light demos
Don’t forget these:
“Floating 100g on water” Beaker with prism and glycerol. Balance a mass on prism.
Dissappearing marbles. Marbles in a flask disappear when viewed from above.
Addition of colours. Cutout circles in card, cover with cellophane. Multiple thicknesses needed for brighter colours (eg
yellow)
“Burning candle under water”. Hide beaker with lit candle behind cardboard screen. Blast screen placed across
trolley. Ask students to look at beaker behind screen, reflection looks like candle is in second beaker. Pour water into
this beaker! (Julius Sumner Miller)
And my students favourite video
“I have a thermal camera and a popsicle”
PFI
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