__Conservation of Energy__

Although the energy can be converted by one form to a different form, the energy cannot be produced or destroyed and this rule is known as the 'law of
conservation of energy' (first law of thermo dynamics). E.g., in a bike, chemical potential energy of the fuel changes to kinetic energy (K.E).

In a radio communication, the electricity is changed into sound (wave energy) and kinetic energy.

The machines can be used to convert energy from one form to another form of energy. While ideal machines keep up the mechanical energy of a system to
maintain, a lot of the energy all of the time turns into heat once using a machine to run. E.g., the heat rendered by friction is hard to gather up and
transmute into a different form of energies. Hence, the heat energy is commonly considered lost or useless.

##
Units of Energy

In the SI (International System of Units), and the unit of energy or work is the J (Joule). Since very small quantities of energy, the erg (erg) is some of
the times practice and an erg is 1 10 millionth of a Joule (J):

##
1 Joule = 10,000,000 ergs.

The power is the range at which energy is victimized and the unit of power is the W (watt) named after James Watt the man who perfected the steam engine
(railway locomotive):

##
One Watt = one Joule/second.

The power is some of the times measured in hp (horsepower):

##
1 horsepower = 746 Watts.

An electrical energy is usually expressed in kWh (kilowatt-hours):

##
1 kilowatt - hour = 3,600,000 Joules.

It's significant to realize that a kilowatt hour is not power it is a unit of energy. E.g., an iron ranged at 2000 Watts would use 2 x 3.6 x 106 Joule of
energy in one hr.

The heat energy is frequently measured in calories quantity. 1 cal (calorie) is defined as the heat needed to raise the temperature of one g (gram) of H2O
from 14.5 to 15.5^{o}C:

##
One calorie = 4.189 Joules.

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