Science Buddies: "Ask an Expert"

Me and my 8 year old son are working on the "How Do Different Materials React to Static Electricity" project. I am in NY, it's perfect weather for this project; cold and dry. We are working on a wooden table. However we have having trouble getting the electroscope to work on other materials. Initially, we followed all the steps, but instead of a balloon, we used my wool scarf and we charged a block of styrofoam and I placed the electroscope on top. The foil ball was attracted to the pie pan and moved toward it. When my son put his finger near the ball it was repelled. We discharged the pie pan and foil ball, as instructed with a screwdriver and then my hand. Then I tried the same steps except using a balloon to charge the wool scarf and nothing is happening....also tried using a balloon to charge saran wrap and nothing happen...I even tried another piece of aluminum foil. I made note of the measurements with the wooden ruler, as instructed, and the only significant change is with the first trial...nothing seems to make the aluminum ball repel from the the pie pan...Am I pairing the wrong items to get this experiment to work...school was so long ago for me, I am at a lost...I appreciate any feedback/ help, thank you.

Assuming you are using this project https://www.sciencebuddies.org/science- ... p023.shtml as a basis for your electoscope design, the following might be helpful:

The sensitivity of the electroscope will be significantly affected by:
1) the mass and surface area of the aluminum foil ball. You want to make it as light as you can; however, you want it to have a lot of surface area.
2) any leakage path. You want to put the aluminum pie pan on an excellent electrical insulator. Something like a clear glass mixing bowl or tumbler or canning jar turned upside down.
3) you don't want air movement or anything else to be moving the ball and causing it to short out against the pie pan.
4) the distance between the aluminum ball and the pie pan. The closer the two are together, the more sensitive the electroscope will be; however, if they touch at any time, the charge beween them will equalize.

If there are an excess of electrons (negative charge) on the pie plate and a loss of electrons (positive charge) on the aluminum ball, there will be an attractive force. If both the pie plate and aluminum foil ball have an excess of electrons, they will be repelled. The same repell will occur if both have a lack of electrons.

When you rub two insulating materials together and a static buildup occurs, one of the materials collects electrons and becomes negatively charged and the other gives up electrons and takes on a positive charge (lack of electrons).

We discharged the pie pan and foil ball, as instructed with a screwdriver and then my hand.

I'm unclear about exactly what you were actually doing electrically. In order to equalize the amount of electrons (what discharging usually means), you really need to temporarily connect the pie plate with something that has a good electrical connection to the earth. If your house uses copper plumbing, then touching the pie plate to a metal kitchen faucet will accomplish this.

Saran wrap is a difficult material to work with. If you "cling" it to the top of a glass mixing bowl before you attempt to charge it, you should have better luck. Try wearing a pair of dry rubber gloves when you rub two materials together and then drop the materials into different glass mixing bowls so the material hangs over an edge but does not come close to what the bowl is sitting on. You can then touch the electroscope to the materials (grounding the electroscope in between) and see what happens.

Figuring out all of the "leakage" paths that can mess up this kind of an experiment is a non-trivial task even for an electrical engineer. Not all material pairs will transfer electrons in a predictable direction and even when you get them to do so, you might not be able to keep the electrons or lack thereof static long enough to measure their effect.