Mechanics

Difference between instantaneous and average power formula

Power definition

The rate of doing work is called power.

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

Average power formula

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

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

Instantaneous power formula

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

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

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

si unit of power

In international system of units the si unit of power is 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 British engineering system the unit of power is horse power “hp”.

Definition of horse power

When a body does work 550 ft-1b in one second is called its one horse power.

Dimensions of power

The dimensions of power are:

Relation between power and force

This is the required relation between power and force.