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In an electroscope, you take metallic balls, and rub them with either a comb or a glass. Touching the balls with your finger is said to undo the effect of rubbing them with the comb or glass, since your finger is connected to ground, and ground is so enormous that it absorbs or releases the electrons to neutralize the metallic ball.
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When you rub your shoes against a carpet and then touch a metallic doorknob, a shock results, since the build-up of electrons that was built up by rubbing against the carpet is released via the doorknob to ground.
What I don't understand in #2 is how the buildup of electrons occurs in the first place. We've already seen in #1 that you are connected to ground, so in #2, why don't any excess electrons released from the carpet at the time of the rubbing immediately go back to ground? (I guess I'm asking a larger question: how can any rubbing of anything create a surplus or deficit of electrons if the thing being rubbed is connected to ground — why doesn't that connection immediately discharge any imbalance of electrons created by the rubbing?)
Best Answer
It's not necessary to go into lot's of details here e.g. whether it's electrons that move or ions, or if it's some energy barrier that prevents a current from flowing or the mobility of ions or whatever. All those details are completely irrelevant to the question.
All you need to look at is resistance, capacitance, charge and current.
If you are charged there is a current flowing from you to ground. The more current flows the faster you get discharged. If the resistance of your shoes + the resistance of the carpet you stand on is relatively low, a high current can flow and you get discharged in a fraction of a second. If the resistance is high it can take a while. When you rub your feet on a carpet, the carpet and also the underside of your shoes become charged. That charge can then flow through your shoes into your body. But if the carpet has a low resistance all the charge will flow away to ground before you get charged significantly. So to be able to receive a shock by walking over a carpet and touching a metal object, you need to have a carpet with a high resistance and also shoes that don't have too high a resistance or else the charge can not flow through the sole into you.
When you touch a charged electroscope it will mostly discharge even if the resistance between you and ground is very high. That is because your capacitance is a lot higher. Capacitance is simply the ability to store charge. The bigger an object is the more charge it can store. So when you touch it the charge will distribute between you and the electroscope but since you are much bigger most of the charge goes to you and the electroscope is left with very little.