Because some of the energy is wasted and the amount of energy wasted is based on the efficiency of the machine
Electromagnetic waves are waves that consist of vibrating electric and magnetic fields. They transfer energy through matter or across space. The transfer of energy by electromagnetic waves is called electromagnetic radiation. ... The two vibrating fields together form an electromagnetic wave.
A snowball picks up speed as it rolls down the mountain.<em> (D)</em>
Since the description includes acceleration ("picks up speed"), we know that the forces on the snowball must be unbalanced.
Power is the RATE at which energy changes or flows.
The unit of energy is the Joule, so a unit of power is the Joule/second.
That unit has the special name "<em>Watt</em>".
Your question is not necessarily a question. It's also a statement, You could write
"<em>Watt's the basic unit of the measurement of power</em>".
