1. I read that there is very high static charge on body making a very high potential on the body. Why don't we feel the shock.

2. Sometimes if we touch the metallic door, only then we feel the shock but not by touching anything else or by rubbing across plastic chair.. Why is it so?

3. What can be total potential across human body, due to static charge.

 

You feel a shock when current flows in your body. When your body has a static charge then there is no current flow until you touch something conductive that is connected to ground.

If the air has very low humidity (cold winter air) so that it does not discharge a static charge on your body and your shoes are an excellent insulator then you can probably build up 50,000V. The discharge current will be extremely low and for an extremely short duration so it will not kill you.

 

You feel a shock when current flows in your body....there is no current flow until you touch something conductive that is connected to ground.

Hmm, I frequently discharge my static electricity through a piece of metal. You then don't feel the current.

We are talking about very low currents here.

To know why nerve cells are being exited when a discharge occurs directly from the skin and not when discharging through something conductive (like a car key for example) you have may have to ask a biologist.

If you touch something that is not connected to ground you can still get a shock.. on a door knob for example. In order to understand the current flow you will need to consider all impedances in the loop.

 

Hmm, I frequently discharge my static electricity through a piece of metal. You then don't feel the current.

We are talking about very low currents here.

To know why nerve cells are being exited when a discharge occurs directly from the skin and not when discharging through something conductive (like a car key for example) you have may have to ask a biologist.
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I actually have built up enough charge walking on a carpet to slight feel the discharge, even when discharged through a metal key.

I think it's related to the area of the discharge. The metal distributes the charge flow over a wider area which keeps the flow through any one nerve below its threshold of feeling.

 

Maybe you feel the heat produced by the spark?

 

An interesting anectdote that I read somewhere about how an author learned about potential static charge in the body. He had a class in a gym where vinyl pads were lining the wall. Classmates would rub against the pads and go shock other classmates by touching them. He discovered that after everybody was charged that the shocks dissapeared. He learned to discharge himself and let all the other kids do the work of rubbing against the pads while he just stood still. He could shock them all.
I thought it was extremely clever for a young kid to figure that out.

 

So question come again, no earth or return point provided still current flows in two separated points. Is it the capacitance in between which gets charged

 

You body can charge to several thousand volts. The charge resides on the capacitance between your body and earth ground. The charge polarity depends upon the nature of the material you rub against that generates the charge separation. Some will give you body a positive charge and some will give it a negative charge. Here's a list of materials with their relative charge polarity.

 

I have found that when static discharges become annoying due to low humidity I can grab a spoon and touch it to the plumbing before I try to turn the water on with my hand. This convinces me that spreading the area the current travels through can completely eliminate the annoying part of static electricity.