Dot Physics

What is this? Number 2

Here is my plan. Post a “what is this” on every Friday until I run out of things. I will post the answer on Tuesday. Maybe we should start keeping points. You get more points for being the first one to get it right. You lose points for getting it wrong.

Last week was easy, but I think this is more of an appropriate level. Here it is:


Nice – it has a tag, but no part number. Honestly, this one stumped me for a while. If you have any reasonable questions, I might answer them.


  1. #1 raidergirl3
    August 27, 2010

    I don’t know, but I have one in my physics lab too! I’ve been thinking it’s electrical, but I’m not sure.

  2. #2 Blaise Pascal
    August 27, 2010

    A couple of questions I think are reasonable:

    1) Does the horizontal metal wire/rod slide horizontally?
    1a) If so, is the horizontal rod bent to become the vertical rod?

  3. #3 Eric Lund
    August 27, 2010

    I assumed that Welch was the manufacturer. A Google search on “welch physics equipment” turned up this website, which plausibly belongs to a successor company. I didn’t find anything looking like that apparatus, but I didn’t spend a lot of time looking, either.

    The metal thing screwed into the right hand side of the body looks like a catch which is designed to hold down the arm which is horizontal in the photo, and both arms are sticking out of a slot in the left side. If you were to free the horizontal arm from the catch, would a spring somewhere in/under the slot pull that arm up?

  4. #4 Rhett Allain
    August 27, 2010


    1) yes – it slides horizontally, not sure if it is supposed to or not thoough.

    1a) Not sure what you mean here. The wire is one piece and fairly stiff. No bending.

  5. #5 Rhett Allain
    August 27, 2010


    I don’t think you are supposed to free the horizontal arm. That cover is screwed down and probably not meant to be unscrewed.

  6. #6 Fran
    August 27, 2010

    I wonder if you could stick different things in the end bits (and secure them with the thumb screws) and then twang one thing and see if the other has sympathetic vibrations?

    This is a total guess since I have never seen one of these before, not in any of the old equipment storerooms I have had the pleasure of cleaning out.

  7. #7 Steve
    August 27, 2010

    Do both horizontal and vertical thingies rotate? When you rotate the horizontal bar, does the vertical bar also turn?

    If so, maybe it is some sort of gearbox to translate rotation about a horizontal axis into rotation around a vertical axis; useful if you have a fixed motor on a workbench (or demo bench).

  8. #8 Rhett Allain
    August 27, 2010


    There are really no moving parts here. There are those little screws (a total of 4) on both ends of the wire and they can turn.

  9. #9 Fruity
    August 27, 2010

    Amperes Rule Apparatus?

  10. #10 Nicole
    August 27, 2010

    I think Fruity has it!

  11. #11 Sili
    August 27, 2010

    Can’t you clean these things while you have them out anyway?

  12. #12 Rhett Allain
    August 27, 2010


    I like to leave them the way I found them. More authentic that way. Who knows how long this has been up in the storage room.

  13. #14 Rabbit Forum
    August 29, 2010

    Isn’t it an Amperes Rule apparatus as pointed out above, sure looks the same.

  14. #15 jim
    August 29, 2010

    It looks like a right angle drive.
    Like to turn something vertically from a horizontal motor shaft.
    The thumb screws would be for quick connects for the input and output shafts.
    Later Jim

  15. #16 scramton
    August 29, 2010

    you can put a compass above the horizontal wire to see the deflection when you run current through

  16. #17 Fruity
    August 30, 2010

    (Mag)-neato! I lurked by the title and gave it a peek. Thought is was actually something else…at first. I’m not at your typical audiences level of physics (unless one physics class 20 years ago qualifies) but learned me something new, nonetheless.

    Thanks for letting me play.

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