Meaning of "pith" in the expression "Pith ball electroscope"

Discussion in 'English Only' started by Ariane, Jun 30, 2007.

  1. Ariane New Member

    Belgium, French and Catalan

    I am a physics teacher in Middle/High School. When we study static electricity, we use "pith ball electroscopes" to test the charge of objects. My question is about the word "pith". What does it mean exactly? Is it the material of which the ball is made? Would native English speakers be able to visualize a "pith ball" just by hearing the word or would they need an additional explanation?

    Basically, a "pith ball" is
    I am not allowed to post the URL where I found this information, but it is the first one that shows up in google if you type in "pith ball".

    A "pith ball electroscope" is simply a "pith ball" hanging from a string. It is used to test whether an object is charged or not. If you bring a non-charged object near a non-charged pith ball electroscope, the pith ball will not move. But if the object is charged then the pith ball will move towards the charged object because it is attracted to it (until they touch, then they will repel).

    I looked it up in the Webster's dictionary and found that "pith" is
    or also
    So, "pith" is usually linked with spongy tissue of plants, citrus fruits, bones or feathers, or with the concept of importance, essential part, vigor, strength. I don't really see how any of these definitions relate to the lightweight black balls I use in static electricity...

    Any help would be much appreciated. This is pure curiosity, but I am fascinated with words and I would love to understand the use of this one.

    Thank you,

  2. liliput

    liliput Senior Member

    U.K. English
    Apparently you can make a pitball from "Styrofoam", I imagine this material has a similar texture to plant pith and perhaps the parenchyma tissue from plants was originally used to make pith balls.
  3. Matching Mole

    Matching Mole Senior Member

    England, English
    Outside of actual vegetable matter, and the abstract metaphorical "pith" meaning core substance of a matter, I would be most familiar with this word in regard to a pith helmet, traditional tropical headgear of the European explorer, and colonial military/police (although more likely to be made of cork rather than pith itself).

    I imagined a pith ball might be a ball made of pith, but not sure of being right, and I think many might be puzzled as to what such a thing might be.
  4. Ariane New Member

    Belgium, French and Catalan
    Thank you very much for your responses. I still don't know the answer for sure, but at least I have an educated guess (a pith ball is probably made of a material of similar texture and physical properties to plant pith).

    I'm also glad to know that students might be puzzled as to what a pith ball is. Sometimes I try to explain words that I think may be difficult for the students and they get impatient because they already know them. So it's nice to hear that this word is not obvious.

    Have a good evening,

  5. lablady

    lablady Senior Member

    Central California
    English - USA
    Hello Ariane,

    I think that the balls were originally made from pith and as other materials came into use, the original name stuck. Benjamin Franklin also used cork. A fun little bit of trivia here.

    There's another reference mentioning the early use of cork here. Matching Mole observed that pith helmets are made of cork. I don't know for sure, but there may be a correlation between the name pith and objects made of cork.

    I cannot find any definite confirmation that explains the name; it's only an explanation based on a very vague memory (dating back to when I took some physics classes a long, long time ago). :)
  6. Packard

    Packard Senior Member

    USA, English
  7. Ariane New Member

    Belgium, French and Catalan
    Hello again,

    Thank you, Lablady, for the nice links. I liked that Spark Museum with all the instruments!

    I made a few more searches through the internet and found another reference that seems to confirm that "pith" refers to the material of which the ball is made. Unfortunately, because I am a Junior member, I am not allowed to send any links.

    The site shows the Triboelectric Series, also called Electrostatic Series, which organizes different materials according to their tendency to attract electrons ("electron affinity") when rubbed with another material. Materials are organized in order of electron affinity, from lowest (tending to lose electrons and become positively charged) to highest (tending to take electrons and become negatively charged). When you want to know what the outcome is of rubbing two materials together, you just need to check which is ranked higher in the list: the one ranked above will become positively charged and the one ranked below will become negatively charged.

    Anyway, here is a part of the list, in case you are interested:
    Here you can see that pith is ranked number 20, along with cork and dry wood. They also show some examples as being sunflower and artichoke stems or elder tree pith.

    Thanks again for everything. I am now going to sleep but I will check tomorrow to see if anyone added any interesting posts.
  8. Ariane New Member

    Belgium, French and Catalan
    Thank you, Packard. I have actually used many pith ball electroscopes for different applications (this is a very simple, yet quite handy instrument). The balls, however, are not all made of the same material, which is the reason why I was wondering what "pith" refers to exactly.
  9. JeffJo Senior Member

    USA, English
    Natural plant pith was the material originally used for the ball, when the instrument was invented, back in the days before plastics. I agree with lablady that it's a case where the old name has been retained, even though the ball is no longer made of pith.
  10. John Carter Banned

    Hi Ariane,
    I can only guess as there seems to be no definitive comment in my reference books and I do not remember the term from Physics study.
    I remember using electroscopes but they were just electroscopes with no additional descriptive.
    My assumption is that back in the old days when electroscopes were first developed 'pith' was the only readily available substance to make the electroscopes from that was both very light and very dry.
    As a physics teacher you will understand that moisture will rapidly cause the electroscope to fail. I assume that they still don't work well on very humid days.
    Perhaps pith is still used to manufacture electroscopes.

    As a written term I consider pith ball to be understandable if somewhat confusing but as your audience will be quite specialised perhaps this is not a problem.


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