# Q & A: Mysterious Charge Collection

Q:
This is gonna sound real strange, and it really freaks me out sometimes. Last year, I was sitting in math class, went up to the board, and while i was getting a piece of chalk fromt the metal tray, I got shocked. Now, here’s the real kicker, the floor is tiled with no carpeting what so ever, and the chairs are wood as so are the desks. Now, recently, this has been happening in other classrooms with the same environment, non carpet tiled floors, wood desk and chair. Why in the world am i and my pupils getting shocked? Told ya it was strange, haha. Thanks!
- ben
A:
While the floor is not carpeted, it can still transfer charges to you when you walk on it. All objects hold onto charges to some degree. If two objects rub together, and one holds charges more strongly, then there is going to be a static build up. A bigger difference in the objects' hold on their charges means greater charge build up.

In your case, the shoe rubber and the tile have different enough grasps of their charges that when your shoes rub the ground as you walk charges build up. Dry air in the room could also contribute to the build up of charges (since charges will dissipate off an object more slowly in drier air).

And, of course, when you touch the large metal conductor on the chalkboard, the charges run off and you feel a shock.

So, while the mystery of the 'math class shocks' is gone, there is still a little suprise waiting for you everytime you go to the chalkboard. :-)

math dan

(published on 10/22/2007)