It's not a bad question, these units of measurements are always a bit confusing. You can similarly ask why for humans, rubbing a balloon is harmless, although that builds up 30 kV of static electricity, while touching a 230 V power socket can kill you.
Voltage is merely the "pressure" that charged particles experience. Voltage alone tells you nothing about how much charge is actually available once electricity is allowed to flow. And that's where the harm comes from. For static electricity, when you touch something, you get maybe a microcoulomb, once, and it's gone. For a power socket, you get up to 16 coulombs per second continuously.
But can e.g. 3V DC kill? Perhaps by using the body's resistance, but I have the idea that the effect would be different from say 220V AC, which affects the nerves.
Not generally, remember Ohm's Law I = V/R. Internally the body has a resistance of ~300 Ohms as a rough rule while our skin is 1000-10000 depending on the condition and contact area involved.
So 3V isn't going to pose any real risk unless it's applied internally and right across a critical nerve leading to your heart or a muscle directly on the heart. For reference pacemakers are generally set to 2-3 volts. Applied externally up to ~12V is generally considered low enough voltage there's a low risk of truly adverse effects.
10 milliamps across your heart can kill but using Ohm's law we can calculate 3V / 0.010 A to get a resistance of 300 ohms. This means you're probably still going to have a bad time if you apply it directly across your heart during open-heart surgery but other than that 3 volts just isn't enough to drive a lethal current through your skin.
Which is why if caught in a lightning storm you should crouch with feet together and why I try very hard to only use one hand when doing something that might have the potential to shock me.
Depends how it's applied and what's sourcing it. 3v does basically nothing to dry skin, but would be quite bad on wires implanted in your chest across your heart.
thats all theory
thing is that I mess with large two volt(nominal)
storage cells,the largest are over 250lbs and sit
like dumb beasts,waiting to oblige anyones low voltage requests,hundreds of amps on tap
be nothing to bolt ,some nice shiny copper handles to the terminals and mist them down with some warm salt water
I also mess around with microscopes,and compared to bugs,humans are very poorly made,so many tiny
things are flawless living perfection,and some like wolf(jumping) spiders are smart,smart enough
that they see us seeing them,and are ok with that
one thing that I have observed that plays into the
static electricity thing,is that many of the tiny
critters that I watch,are impecably clean,no dust
or dirt on them at all,perfectly clean,unlike a human finger,which is one zillabutt uggly thing,under magnification
Voltage is merely the "pressure" that charged particles experience. Voltage alone tells you nothing about how much charge is actually available once electricity is allowed to flow. And that's where the harm comes from. For static electricity, when you touch something, you get maybe a microcoulomb, once, and it's gone. For a power socket, you get up to 16 coulombs per second continuously.