Custom Search
Power
Power is a measure of the rate at which work is done or energy converted
Sponsored Links
Work done
Power is a measure of the rate at which work is done and can be expressed as
P = W / dt (1)
where
P = power (W)
W = work done (J)
dt = time taken (s)
Work can be expressed as
W = F s (1b)
where
F = force (N)
s = distance (m)
Since work is the product of the applied force and the distance, (1) can be modified to
P = F v (1c)
where
F = force (N)
v = velocity (m/s)
Energy converted
Power is also a measure of the rate at which energy is converted from one form to another and can be expressed as
P = E / dt (2)
where
P = power (W)
E = energy converted (J)
dt = time taken (s)
Example - Power needed to lift a Mass
A mass of 1000 kg is lifted 10 m in 10 seconds.
The work done can be calculated as
W = (1000 kg) (9.81 m/s2) (10 m)
= 98100 J (Nm)
The power required can be calculated as
P = (98100 J) / (10 s)
= 9810 W (J/s)
Example - Work done by Electric Motor
The work done by a 1 kW electric motor in 1 hour can be calculated by modifying (1) to
W = P dt
= (1 kW) (1000 W/kW) (1 h) (3600 s/h)
= 3600000 J
= 3600 kJ
Sponsored Links
Search the Engineering ToolBox
Custom Search
Engineering ToolBox - SketchUp Edition - Online 3D modeling!
Engineering ToolBox - SketchUp Edition - enabled for use with the amazing, fun and free Google SketchUp