Electrostatic Lab: Rub a Balloon for Styrofoam Repulsion

[shawshank]

Rub a balloon containing a few pieces of Styrofoam towards your sweater or a piece of wool/fur. What do you observe when you touch with your finger one of the piece through the balloon? Why does this happen?

The Styrofoam repels within the balloon. You charge the balloon negative by rubbing it against your sweater and the electrons of the neutral Styrofoam are pushed as far as possible from the walls of the balloon making the side of the Styrofoam touching the balloon
positive. When you put your finger on where the Styrofoam is touching the balloon, you are grounding the electrons on the surface of the balloon into your hand and making that spot on the balloon positively charged. Since the side of the Styrofoam touching the balloon is charged positive and you've made that spot positive, the Styrofoam repels.

Am I on the right track or just talking crap?

 

[shawshank]

please help it's due tomorrow ;(

 

[shawshank]

:( :(

 

[andrevdh]

Electrons will flow into the surface of the balloon and the positively polarized region on the styrofoam where you touch it. This means that the surface is neutralized where it is touched, but the styrofoam is effectively charged negatively by induction. The rest of the charged surface of the balloon then repels the styrofoam.

 

[shawshank]

Why would electrons flow onto the surface of the balloon, shouldn't they flow off into my finger since the balloon is negatively charged.

 

[shawshank]

If anyone is online, this is due in an hour. thanks

 

[shawshank]

dammit, it's due in 30 mins :(

 

[shawshank]

Ok, I give up. Going to hand this in. Andre I kind of got what you mean, but I can't see how electrons will flow from the balloon into the Styrofoam (they're not conductors) and why electrons would flow onto the surface of the balloon when it is already negatively charged in that spot.

What I wrote is that the finger neutralizes the spot you touch through conduction and the paper no longer feels attraction at that point since both objects are neutral. However, the charges of the Styrofoam have been polarized so when you destroy the attraction to the wall, that side of the the Styrofoam (the side away from the wall) is repelled by the still existing negative charge on other spots on the surface of the balloon.

 

[andrevdh]

The styrofoam sticks to the wall due to its opposite polarization by the charged wall of the balloon. When one touches the balloon it becomes locally neutralized - also the side of the styrofoam that is positively induced. This removes the sticky connection between the wall and the styrofoam, but the styrofoam now has a net negative charge and it is repelled by the wall.