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Okay, don't laugh, my 13 year old needs a science project done by weeks end. Here is what we've come up with, I just feel there has to be something better in the way of Science, than just proving the pounds of force pull on a guitar top, tuning six medium 80 / 20 Bronze strings to pitch. Open for suggestions from one and all.

The hypothesis: An attempt to show that there is more than 100 pounds of force but less than 200 pounds of force needed to tune an acoustic guitar to pitch. Lame I know.

Here is a pic of the jig. It traps the ball end on the frame, comes up and over two super glued bone nut/saddle arrangements, then down to awaiting weight holder which isn't made yet. You add weight until the pitch for that string is reached and record the weight amount. After all six, you add them together to get the total force. Now, is this really science or not?

Anyway, as you can tell, we need help.

Oh this is a 25.5" scale, uncompensated.

Hey, this doesn't look lame at all. Should be a fine project.

Grant Goltz

Fine lookin young man there Bruce. You should let him have some Ebony and Rosewood for his project though, Gotta impress the ladies.

What will you use for weights?
Or maybe if you have a set of fishermans scales you could probably use those and put a tuning peg on the apparatus.

Interesting. Was just discussing with my 11 year old her Science projects ideas and am looking for sugestions. She was thinking of doing something about the tonal properties of different woods or on relative strengths and applications of different glues. Any ideas on good experiements for these or on other related ideas?

If your son handles basic algebra well (I'm not sure what at age that is
taught) he may enhance the project a little by testing different strings.
You could test D'Addarios against DR's, or a plain steel .020" against a
nickel wound .020", or little things like that.

It looks like a great project - it looks an awful lot like old sketches of
tools Pythagoras used 2500 years ago.

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Eschew obfuscation, espouse elucidation.

Have you thought about a wheel or pulley at the lower end to eliminate friction? Might make a difference, but then again, might not.

Pat

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now known around here as Pat Foster
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http://www.patfosterguitars.com

Hmmmm, maybe we could collaborate....

arvey:
How long before the Science Fair?

Tonal properties of wood is a pretty big subject: it's not too hard to measure mechanical properties, like Young's modulus, density and damping, that _effect_ tone, but correlating those properties with the way the guitar sounds is trickier.

If you have a small budget for a few little 2W amps and some electronic know-how you could look into what changes in a piece of wood that gets vibrated for a while. The neat thing about that is that it would be _real_ science; there's almost nothing in the literature about it that I know of.

On the simple side, how about a project involving measurements and playing tests to look at the relationship between soundhole size, low-end resonant frequencies, and the bass tone of the guitar.

There are lots of good projects, depending on how much time and skill you've got to work with.

Pat, That is a good idea. We simply made an oversize groove in the bone nut, plus we graphited the groove with a pencil. But the pulley idea is a good one to eliminate the drag especially in the larger wound strings.

I wish we had some formulas for the force created by the weight and the stored energy.

DL, We considered Bubinga veneer overlays, looked at each other intently and said, "Nahhhhhhhhhhhhhhhhhhhh."
But we did consider it.Dickey38733.3715509259

How about just building a volcano with vinegar/baking soda 'lava' or making a styrofoam ball model of the universe instead? Just kidding. Those things have been universally banned in our school's science fair.

Actually, I'm getting my students ready for the science fair at school later this month. What I tell them is that they need to ask a question or define a problem and then use an experiment to find the answer. They should not just perform a demonstration.

In your case, your rig would work, but you need a question. David's post is a good example of a question. You could also ask something like, "Why does the manufacturer prohibit heavy strings on my guitar?" Then you could use your rig to test the pull of a set of light, medium, and heavy strings. Your test would then show the amount of pull exerted by each set of strings, and your conclusion would be "...heavy strings exert xxx pounds of force rather than the xxx pounds exerted by the manufacturer-recommended light strings."

Hope this helps. Let us know how it turns out.

Bruce, this lame science project now jumps to light speed! I knew there was someone on the OLF with the right background to kick this project in the pants!

Thanks a million. He's out for teacher's meetings today and we'll jump on this with both feet, er, all four feet! Udaman!

David, I missed your post, sorry. Yeah that Pythagoras had it going on now. In construction, I used his work all the time. The 6-8-10 Squaring Method is something every carpenter should know. Also, we learned that solving for a hypotenuse equation is your friend!Dickey38733.4272337963

The force is easy to calculate from the weight used to stretch the string.

The stored work in the non-vibrating string will be a function of the force and how much the string has stretched. You could simply measure the stretch: mark where the string goes over the 'saddle' when it's just tight enough to be straight, and then see how much string has pulled over the saddle when it is brought to pitch.

Energy is work/time. Compression waves travel very fast in the string, so when it breaks at one end the other finds out pretty quickly: probably about 1/8000 of a second for a 'normal' string length, and all the energy gets changed from potential into kinetic in that time. Now you see why the end of the string moves so fast when it breaks.    

In Canada we just use the 3,4,5 rule for squaring and just double it!

Shane

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Canada

Hey Bruce
     Here is another thing you can try and show
1 the rotaional force on the saddle
2 the resulatant load on the neck.
   You plot the string angle based on a line from the base of the nut to the saddle base ,then you can figure the angle and the resultant forces created by the strings. The forces are not just in one direction.
    Ohhh the love of Math and science
john hall

Headed out to eat, we are finding some surprising results. More later. Basically, it takes more tension to tune a string than we've been told.

This has taken all day and we're not done yet.

Yeah, Shane, 3,4,5 is all we learned at my school too. But, hey, we were a small school.

Ron

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OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

Allen, there is still a good 2 months till my daughters science fair so right now she is trying to "find the question" and devise the investigation. Last year she won both the local and regional science fairs (couldn't aford the $2000 to go to the provincials) so she has a lot to live up to. She is also thinking about trying to find out if "fish have only a 5 second memory" as her teacher told her. But she thinks it would be cool to do something related to dads work. She is also thinking of the question "is a glue joint stronger than the wood" and then look at different kinds of glue under different types of onditions.

Surprising Results, who knows how the stringmakers test the tension required by their strings? We got way more tension on each string than the manufacturers say is required.

An amusing note, we were about 1/3 done with testing, we started with a set of Martin Mediums, then switched to D'Addario Lights for that guage. Printed right on the back of the package is the tension required to tune each string! No kidding.

We are glad that we tested though, my son, and I for that matter were blown away by what we found. Here are the totals.

Light Guage 202.5 lbs

Medium Guage 227.5 lbs

Heavy Guage 271.9 lbs

The heavy guage exerts 69 lbs more pull than the lights.
The medium guage exerts 25 lbs more pull than the lights. That is a lot of tension.

These tests took hours to perform. I was proud of my son's tenacity to stick with it. Now for some incredible individual string reads.

We had one anamoly, a .045 medium A string that required 48.4 lbs to tune it to pitch. It didn't fit the pattern of the other strings, so we retested using another .045 medium A string, that one while still high did drop six pounds to 42.2 lbs.

I guess for it's size, we were most amazed by the G string of the medium set at .026 guage, it required 46.2 pounds of tension to pull it to pitch. No wonder those things really zing when they break. We also found out that, that particular string, has a .013 inner core, the same as a medium high E string, .013.

So that about does it for testing. Pat Foster is probably right, we should have used a pulley. I'd love to know how manufactures arrive at their numbers. I'm sure our crude setup, had something to do with our higher numbers.

Not only did we test a bunch of strings, we made a memory on my son's day off of school. His brother drove 90 miles from a neighboring college town to bring him a set of heavy strings which are hard to find by the way. You have to either special order them or buy them as individual strings, which is what we did.

Okay, the two strings tied for the most pull, the heavy D and G strings weighed in to pitch at 57.4 pounds of force. We used a piece of Romex, an old weight-lifting set, a bolt which we wrapped the string around and bolted the weights too. Time consuming, and made a loud crashing sound on two strings that broke in process. Watch those toes! We considered the fishing scale inline, but decided that the scale was too small to read accurately.

Thanks for all the suggestions.

Bruce,

What a great project to do with your son! Thanks for sharing results.

Pat

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now known around here as Pat Foster
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http://www.patfosterguitars.com

Bruce, I think BruceH really had a good idea.
It struck me that you could include a demonstration with your presentation. Your son could take one of your guitars, string it with heavy guage strings, then as he brings it up to pitch, show the class how the thing implodes. Or, how the bridge pops off. Or some such dramatic display. That would prove the need for science.

(Now I'm messin with you!)

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Bruce...just a thought...in the pic where your son is tensioning the wound string. Does it matter that the string is held on the unwound leader...or would it be more appropriate to clamp on the wound portion?

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JJ
Napa, CA
http://www.DonohueGuitars.com

Thanks guys, Gee JJ, I don't have a clue. The Heavy set were made up a string at a time in a distant city. Some of them were barely long enough to get hooked up as it was. So, while we were attempting accuracy, I'm sure there are factors such as this that make a difference in the real world.

You'd think the tensions would be uniform as you go from .o12 to .014 to .016, but as we went we found some strings that actually went out of bounds either higher or lower than we expected. We tried to guess each time based on data we'd already collected on how much weight we needed.

Fortunately, only once did we put on too much weight to start with, usually we were four or five frets low and could inch our way up. One time out of 18 we were a half semitone over. I think the fact that our setup required a 45 degree break angle to the weights, that may have caused our readings to be a bit high.

To repeat the project would be to play with that angle and possibly install a small pulley to eliminate that issue. We had fun and learned which strings to look away on, as we tune...... grin.

D'oh...nevermind. I was thinking that the end point was string breakage...and failed to realize that it was tuning to pitch. I need to read more closely.

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JJ
Napa, CA
http://www.DonohueGuitars.com