Power
"P"
What it is
Energy is the capacity to do work, and power is how how fast the work is done.
To accomplish the same amount of work ten times faster, you must dissipate ten
times the power. Real power is the amount of power leaving an isolated system.
The real power in a pendulum system is that power which is being converted to
heat by friction and wind resistance. Apparent power is power that stays within
a closed system but changes form with time. The apparent power in a pendulum
system is the power that is exchanged between momentum and gravity. This power
stays in the system until dissipated by friction at which time it becomes real
power. There can be no real power in a completely isolated system, as all of the
energy stays in the system.
History
James Watt (1736-1819) was very instrumental in promoting the use of steam
engines to replace water power and beasts of burden. He learned to evaluate his
engines in terms of the horses they replaced and the amount of fuel they
consumed so he could sell them to potential users. He learned much about energy
( food for the machines) and power ( how fast they could work) and like
entrepreneurs through out history transmitted this information to his customers.
James Joule(1818-1889) established the relationship between electrical power
and heat. He determined that the amount of heat produced each second in a
conductor by a current of electricity is proportional to the resistance of the
conductor and to the square of the current.
power = resistance * current^2
Common equations
power = energy / time
Power = force * velocity
power = voltage * current
power = electric field strength * magnetic field strength * area
Units
watts
erg per seconds
calorie per hour
horsepower
ft-lbs per second
BTUs per minute
force de cheval
lumen
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