Superpositioned

1. In the first scenario, the piano is suspended above our stick figure with some amount of stored energy. Because the piano is suspended, it poses no danger to our stick figure.
2. In the second scenario, the piano is released, and the stored energy is converted to motion. The piano is now potentially lethal.

Similarly, voltage is of no danger unless your body completes a circuit (if you are touching the ground) and a charge is able to flow through your body.

Effects of current on your body

There are several factors that influence current’s effect on your body. First of all, everyone has a unique chemistry so the effects are different for everyone. In fact, the small difference between a man’s body and a woman’s body cause significant variations. Secondly, the frequency of the current plays a critical role. The human body’s nervous system and muscles communicate using a frequency of 50-60hz making us extremely susceptible to current at this frequency. High frequencies and direct current are not as harmful.

The tabulated effects of current on the human body:

BODILY EFFECT     DIRECT CURRENT (DC)    60 Hz AC     10 kHz AC
--------------------------------------------------------------- 
Slight sensation     Men = 1.0 mA         0.4 mA        7 mA 
felt at hand(s)    Women = 0.6 mA         0.3 mA        5 mA 
--------------------------------------------------------------- 
Threshold of         Men = 5.2 mA         1.1 mA       12 mA 
perception         Women = 3.5 mA         0.7 mA        8 mA 
--------------------------------------------------------------- 
Painful, but          Men = 62 mA           9 mA       55 mA 
voluntary muscle    Women = 41 mA           6 mA       37 mA 
control maintained                                           
--------------------------------------------------------------- 
Painful, unable       Men = 76 mA          16 mA       75 mA 
to let go of wires  Women = 51 mA        10.5 mA       50 mA 
--------------------------------------------------------------- 
Severe pain,          Men = 90 mA          23 mA       94 mA 
difficulty          Women = 60 mA          15 mA       63 mA 
breathing                                                    
--------------------------------------------------------------- 
Possible heart        Men = 500 mA        100 mA             
fibrillation        Women = 500 mA        100 mA             
after 3 seconds                                              
---------------------------------------------------------------

Ohm’s law (V = I*R)

Ohm’s law, voltage = current * resistance, is the deadly relationship between current and voltage. Basically, if you connect a charged source to ground, the current through you is going to be directly proportional to the sources voltage. Therefore, a high voltage differential causes high current. The amount of current is indirectly dependent on your resistance.

The human resistance factor

Unfortunately, the human body makes a horrible resistor. Because we are composed mostly of water inside, the majority of our resistance is in our skin. Personally, my hand-to-hand resistance is about 540 k-ohm. Wetting down my fingers reduces my skins resistance and drops this number down to around 60 k-ohm. This is why you never want to be wet around electricity. Nine times more current is able to flow through my wet skin at the same voltage!

Why birds can stand on power lines

On simple property of electricity holds it ground in the example. Current prefers the path of least resistance. It would rather flow through the wire than the bird, which has a relatively high resistance compared to a power line. However, a charge always wants to obtain and equilibrium. If an object connects a charged line to a source with less charge (say the ground), then this becomes the easiest path for the source to discharge itself.

How an electric fence works

While I am writing, I should dispel another rumor. Most people assume an electric fence has current flowing from one end of the fence to the other when in fact it is charged uniformly from both ends. There is no significant current flow until you complete a circuit to the ground. In fact, the unit that powers an electric fence is sold as a ‘fence charger.’

This is a common misconception because common electric fences have a pulsating voltage. There is in fact a small current flow as the fence is charged and discharged, but the flow is not from one end of the fence to the other. It simply in and out of the fence.