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## Physics library

### Course: Physics library>Unit 18

Lesson 8: Electrostatics

# Pith ball electroscope

Primitive device for measuring electrostatic force. Created by Brit Cruise.

## Want to join the conversation?

• Could we measure this force using the angle of deviation away from the rest position(in radians or in degrees)?
• The main problem I can see with that is: what if something has more charge than the plate? It would only be able to pull it so far before there's no difference, yet the objects could have completely different fields!
• That was cool. But did any of you see that as the guy was rubbing the plate on the cat, the cat got up and tried to get away? LOL I would too. ;)
• How is a stick able to hold an electrical charge to produce static electricity? Also, what kind of ball is that and how does it become attracted to static?
• I think Sal might have some videos on static electricity.
That's a pith ball and it's made from the dry, spongy material found inside the stem of some plants. It holds electricity for the same reason that your hair stands on end when you rub a balloon through it. Hope that helps!
• we could measure the force in a standard unit by adding weight to the Styrofoam ball and then test how powerful the static is by how much weight it could hold
• What if 2 balls (ignoring gravity) attached to a string and possessing same charge (say, +q) are suspended. What will be the angle (theta) between the strings and also tension in strings?
• You said, "ignoring gravity." In electrics, where opposites attract, likes repel. The balls move apart. Unobstructed, the balls assume an orientation as far from each other as possible. This is likely a theta of 180º in your system. The key is the "why?"
Theta is most useful, in the gravity case.
• What is the "Pith Ball"? What is it made of?
• This is a styrofoam ball, though you could also use a small piece cork.
• how could we measure this force with unit standard unit?
• What happens when you the pipe like structure to the cats fur?
(1 vote)
• What is the material is the man rubbing against the cat, which he uses it to attract the styrofoam ball?
(1 vote)
• Brit used plastic straw then a plastic plate.
(1 vote)
• Then do paper plates has any charge?
If so can we use normal reading paper?
(1 vote)

Starfor topu