Physics

drift velocity = v_d = \frac{eE}{m_e} \tau

I = v_d A n e = \frac{e^2 n \tau}{m_e} A E

Conductivity = \sigma = \frac{e^2 n \tau}{m_e}

V = \frac{l}{\sigma A}I

Resistivity = \rho = \frac1{\sigma}

Resistance = R = \frac{l}{\sigma A} = \frac{l \rho}{A}

V = IR

Ohm's law doesn't hold when current causes temperature change (thus changing resistance)

Adding ions to air or water increases its conductivity

Shoes have a resistance of about 4 billion ohms, but is still too high to prevent discharge of static electricity (high voltage, low charge).