Power is calculated by multiplying voltage by
a. current.
b. energy.
c. resistance.
d. voltage.

If you're calculating the power of an athlete who is lifting weights,
or the power of a windmill that is pumping water from a well, or
the power of two horses turning millstones, then those electrical
units won't help at all.

But if you happen to be calculating the power delivered to an
electrical circuit or dissipated by an electrical device, then you
can use ...

                (voltage) times (current)
or
                (voltage)² divided by (resistance)
or
                (current)² times (resistance) .

The choice just depends on which quantities you know
or can easily measure.  

If there was no gravity then their would be no downword force on the football to have it return the the grownd, and if there was no friction (mainly air friction) then there would be no opposing force the stop the ball from moving through the air allowing the ball to travle ∞.