Work

$W = (F \cos\theta)d = Fd$
where $\theta =$ angle of force to direction of movement
No work : displacement = 0, force = 0, force $\perp$ displacement
SI: 1 joule = 1 n$\cdot$m = $1 kg \cdot m^2/s^2$

Energy (measured in joule/sec)

Ability to perform work
Neither created nor destroyed, only transformed
kinetic ~ = energy in motion
potential ~ = energy stored by object.
Measured by amount of work done.

Power

Rate of doing work $P = W/t$   where $W = Fd$
Unit: Power doesn't have direction $\Rightarrow$ scalar
Watt = joules/sec (j/s) = $1 kg \cdot m^2/s^2 = .24 c/s$ (calories/sec)
    = Power need to do 1 joule of work in 1 second

$P = VI$ or $P = VA = V^2/R$

Electrical Energy

Unit: joule = watt$\cdot$sec (w{\cdot}s)
    = 1 amp. of current flows through the circuit for 1 sec. when the potential different of 1 volt is applied across it.

$1 kwh = 36 x 10^5 w{\cdot}s$ or joules.