The rate of doing work is called power. The basic difference between average and instantaneous power is that average power is the ratio of total work and total time. While instantaneous power is the limiting value of average power.

From the statement of work, it is not clear whether that same amount of work was done in one second or in 1 hour. The rate at which work is done is often interesting in practical applications.

## Power formula physics

## Average power formula

The ratio of total work to total time is called average power. Mathematically it is expressed as

If “ΔW” is the work done in time “Δt” then the average power will be:

## Instantaneous power formula

The limiting value of average power such that Δt approaches zero is known as instantaneous power.

If “Δt” approaches zero then power will be instantaneous and given by:

ΔW is the work done in a short interval of time Δt is following the instant t.

## si unit of power

In the international system of units, the si unit of power is the watt.

## Watt definition physics

Watt is defined as:”When a body does work of one joule in one second is called its one-watt power.”

**1 watt = 1J/1S**

The multiples of power are KW, MW, GW…

In the British engineering system, the unit of power is horse power “hp”.

## Definition of horsepower

When a body does work 550 ft-1b in one second is called it’s one horsepower.

## Dimensions of power

The dimensions of power are:

## Relation between power and force

This is the required relation between power and force.