# Electric discharge due to fricition

Consider a person wearing rubber shoes sliding his foot against a woolen carpet.

When the person touches a metallic door handle, he gets a shock due to the discharge of charges accumulated on the shoes. First, the rubber shoes develop a negative charge. So how does the person get the shock if the electrons are moving out of his body and not come into it?

Also if charge on the shoe is supposed to be static due to the fact that rubber is an insulator, then how does it move from the shoes to the door handle. Is it due the fact that our body is a conductor? If so, how do the electrons know that there is a path available for them to flow through i.e. the metallic handle.

Next consider, if a positively charge glass rod was brought close to the shoes before the handle was touched. Would the negative charges be attracted to the rod or remain static?

• Hint: When two terminals of a battery are connected by a wire, how do electrons at one terminal know that they have to flow to the other terminal ? – user135951 Dec 16 '16 at 15:17
• @Doraemonドラえもん If you mean a potential difference, that would imply some residual charge would still be left on our body right? Because the charge would only flow till the potentials equalize. Consider the metal handle is attached to a rubber door in this scenario so that the charge on the handle doesn't flow anywhere :3 – LeroyJD Dec 16 '16 at 15:28

Electrons' directions in not important: both if they enter your body and if they go out from your body they are responsible for a current and all the consequent physiological effects on a human body.

Some years ago, I made a similar question to my professor of electronics: why do I get electric shock if I touch a fence for cows, despite I'm wearing rubber shoes? Well, the answer was "Our body, the shoes and the ground are a sort of capacitor". To be more precise, the lower part of your shoes, i.e. the soles constitutes one plate of the capacitor, the central part of the shoes constitute the dielectric and our body, namely our feet constitute the other plate of the capacitor. While you are walking on a wollen floor, some charges get stuck on the soles. These charges create an electric field which attracts charges from your body and makes them accumulate on the bottom of your feet. But these charges cannot cross the shoes, due to their insulating properties. We have a capacitor?! Don't we? When you tuch a metallic object, maybe connected to ground, with your hands, the excess of charges is immediately compesated by an incoming/outgoing current. That's why you fell the shock.

Eventually: if you succeed in discharging the soles of your shoes before touching the metallic handle, you discharge the capacitor before connecting it to the ground and so when you touch the metallic handle you shouldn't feel any shock because no currents will be flowing.

• Okay so consider @Maximus 's answer. If there is a charge separation, say the negative charge at our fingertips comes into contact with ground and it gets neutralized but the positive charge still remains in place.... so as a whole if somehow the negative charge on the soles were discharged... our body as a whole would be positively charged? – LeroyJD Dec 20 '16 at 15:10
• In our simplified model the soles are insulator and don't let electric charges flow in/out human body. – AndreaPaco Dec 22 '16 at 1:01

So how does the person get the shock if the electrons are moving out of his body and not come into it?

When electrons pass from your body to another object, they tend to move in/out in very tight clumps. So for a very tiny area, there are many fast moving electrons and thus, heat. Heat is independant of electron direction (at least on macro level.)

Also if charge on the shoe is supposed to be static due to the fact that rubber is an insulator, then how does it move from the shoes to the door handle.

We are conductors. See this:

If so, how do the electrons know that there is a path available for them to flow through i.e. the metallic handle.

Electrostatic forces. That's all we know.

Next consider, if a positively charge glass rod was brought close to the shoes before the handle was touched. Would the negative charges be attracted to the rod or remain static?

According to picture, step 3, I would suggest that you would be less negatively charged on your hand, so, may not even get electrocuted when touching the handlebar.