Thermal Expansitivity of Hard Wood

1. May 5, 2004

Esco

hey wassup every1.my first post lol.neway, ive got a question which i cnt seem to find the answer to anywhere else so im hopin one of u lot could help me out. anyway heres the question. How do i find out the percentage error of a hard wood ruler compared to the actual graduations of the ruler which are 1mm. basically i am measurin the length tht an air column rises using a hard wood ruler dipped in cold water then gradually risen to 100degree c.so the range is 0-100degrees. so how do i obtain the thermal expansitivity of the co-efficient of the hard wood and then use tht to work out the %error created by the ruler.my starting length of the air column is 54mm.if u dnt understand the question cuz i ent worded it properly then its all gud, but cud sum1 tell me the thermal expanisitivity co-efficient of hard wood.thanx all.word up.

2. May 5, 2004

Integral

Staff Emeritus
Try doing a web search on Young's Modulus.

Off topic:
I am somewhat put off by your flagrant disregard for the English language. Correct grammar makes it much easier to read and understand questions. If you cannot show such a basic courtesy to the audience of your question, it is not clear why we should but any effort into our responses.

I am aware that my grammar is not always perfect but at least I try. Please but some effort into writing a message that does not require an interpreter to read.

Edit:
My memory must be failing, I was unable to see the direct connection between Young's modulus and the Coefficient of expansion, that I seem to remember. Do your web search on The coefficient of expansion. Good luck wood is not a commonly listed material.

Last edited: May 5, 2004
3. May 5, 2004

Esco

yeh but the thing is, if i did wanna talk with regards and talk in full words and not abbreviations then i think id be doin an essay, cuz i do enuff english in college as it is let alone come here and start again, fair comment tho i respect it, but i somewhat feel uneasy when you directly use irony to try and mock the way i write my stuff down.oh and another thing, i think i do hav regards to the english language when i have to.1.

4. May 5, 2004

Bystander

jsl dsi kekhjtnc kskut a 1 - 30 ppm aldi l.e,.ma.. But, if you want a number for the exercise you're working on, a ma lei ma;'adliujmm ,, a; apr a; 10 ppm/K.

Don't post this kind of crap in two forums --- most people here read more than one at a time --- you a pre-med or somethin'?

5. May 5, 2004

Cliff_J

A wooden ruler in water? Better have a good varnish on it or the expansion will not occur only from the temperature change but from the swelling as well. A plastic one that doesn't get soft at 100C would be an ok choice, a metal ruler would be the easiest to find the coefficient of expansion on and the likely best choice.

And is it that much more difficult to use regular english instead of some text-chat garbage?

6. May 6, 2004

Esco

by stander u said... jsl dsi kekhjtnc kskut a 1 - 30 ppm aldi l.e,.ma.. But, if you want a number for the exercise you're working on, a ma lei ma;'adliujmm ,, a; apr a; 10 ppm/K.

i have no possible idea of what you are talking about. could you please state what you are saying more clearly again please.thank you.

7. May 6, 2004

Staff: Mentor

f u cn rd ths

Ah... so you do speak english!

Who knows what you are looking for, since you are too lazy to write clearly. I'm guessing that you would like to estimate the possible error in length measurements due to thermal expansion of your wooden ruler? Well... get two rulers and measure the expansion yourself. Keep one at room temperature, then cool the other and compare them. Then heat it and compare. That will be more useful that any book value.

Why are you using a wooden ruler in water anyway?

8. May 6, 2004

Esco

Thank you Doc Al, i never actually thought of doing that. Well i am investigating Charles Law. Using the method of achieving an extrapolation for absolute zero by obtaining the change in volume of a column of gas in a capillary tube as the pressure is being kept constant as the temperature is being decreased. As volume is proportional to the length i am using a wooden ruler to measure the change in length. I decided to use wood rather than steel or aluminium due to these materials being good conductors of heat. Plastic would melt near 100degreeC, so i decided to use hard wood. I have found out the co-efficient of Hard Wood, but now i need an equation which shows me the expansion when i have increased the temperature from 0-100degreecC. My initial length of the mercury thread was 54mm which is used to keep pressure constant and also a marker for the indication of the length rise. So DocAl would you be so kind as to state the equation for this. I know this is a crude experiment to do to find absolute zero but it is sufficient for my coursework. Thank You.

Sorry about the abbreviations in the initial question, i did not know people would take offense to it. Thank You.

9. May 6, 2004

Staff: Mentor

Try this, where α is the coefficient of expansion:
$$\Delta L = \alpha L_0 \Delta T$$

10. May 6, 2004

Bystander

Do you have access to a copy of the CRC Handbook of Chemistry and Physics? If so, edition doesn't matter too much, check the index for "expansivity," and hunt through the half dozen entries for "thermal expansivity of various materials" to see where it's located in whichever edition you happen to be using. Voila! you will find an entry for "hard wood" (whatever the hell that is) as 10 ppm/K from 0-100C. You will also notice the wide range of expansivities for various varieties of woods --- this is compounded by mother nature's slovenly habit of growing no two trees the same way, nor of growing wood on one side of a tree with the same properties as on the other side.

10 ppm/K times 100 K difference in temperature extremes? 0.1% error if you ignore it; this is probably 5-10 times less than the uncertainty in the ruler itself. Yeah, it's good practice to account for it. It's a source of error that you have recognized --- once it's an order of magnitude less than other error sources, you are perfectly (Not for some lab instructors in my past, nor for myself when I was TA'ing....) justified in stating it, estimating its contribution to overall uncertainty as insignificant, and moving on with the analysis.

Isn't English much more useful for communicating scientific/technical concepts? I'd give you a smilie here, but I ain't quite figured the trick in the "new" editor.

11. May 6, 2004

Integral

Staff Emeritus
Just a note, my Handbook of Chem and Phys. 53rd ed did not have the information, it was the first place I looked.

12. May 6, 2004

Bystander

The "old" format, includes trig tables and other arcana, vs. "new" (post pocket calculator) format is/was infinitely more useful. CRC shot 'emselves in the foot/flipper bigtime. The Ooolllllddddd 5x7 format is the good one --- was thoroughly proofed and corrected --- no really bad numbers in it, archaic, but not incorrect. Last ten years? CRC makes a good doorstop --- the chemical properties tables can't be trusted much further than the anarchists' cookbook (anarchists' or, anarchist's?).

13. May 9, 2004

Gokul43201

Staff Emeritus
Can you not use a graduated glass capillary, or mark off the various positions on the capillary and measure them later ? That way, your ruler is not interacting with your experiment. Keep in mind that your glass itself will be expanding but this is true in any case.

You will get nowhere using expansivity data for wood - there's a huge contribution from moisture.

14. May 9, 2004

Gokul43201

Staff Emeritus
If you are at a univ. that has access, you can use the CRC online at hcpnetbase.com

15. May 9, 2004

flexten

hbcpnetbase.com

16. May 18, 2004

Esco

yo thanx all that helped me. its much appreciated. thanx again.