In physics, **power** refers to the rate of transfer of energy respect to time.^{[1]}

Mathematically, average power is expressed as:

P = *W* / Δt

Therefore, power at any instant can be determined by the equation:

P = lim_{Δt->0} *W* / Δt = dW / dt

Since d*W* = F dx and v = dx / dt follows that:

P = F · dx / dt = F · v

The usual units for power are Watts ( W = J/s ) and horsepower ( hp = 746 W )

## References

- ↑ Serway and Beichner,
*Physics For Scientists and Engineers*, Fifth Edition