I've been thinking about this conundrum.
Given we use joules to move a metal block over a surface, we do work.
So imagine a motor, that spins and pulls a string, moving said metal block over one meter toward itself.
We supply it with 1 volt, 1 amp and it needs 5 seconds of time to do the work of pulling the block for 1 meter.
Given volts are J/C and amps are C/s, we can say volts are how much work, certain amount of electrons will do, over time. And volts * amps are work over time or J/s.
So, 1 V × 1 A × 5 s = 5 Ws = 5 J
Now the question is:
How much energy of 5 J was used to move the block, and what amount was spent on heating up the wires?
Am I right to think, that since 99% of resistance is taken by the motor, it leads to firstly meaning 1% of all energy spend goes to heating up the wires, and secondly (imagining a 80% efficiency motor) ~80% of those 5 joules are spend on moving the block and ~20% of those 5 J are heating up the motor's insides?
In retrospect, we can ponder about how much energy gets spent on friction between the block and it's supporting surface, but I digress.
Your input on this, is greatly appreciated. Thank you.
Best Answer
If the motor is 80% efficient, 20% of the electrical input is used to heat up the motor (internal wire and iron) and 80% is used to supply mechanical energy to whatever is connected to the shaft. That is mostly correct. A small amount of the lost energy is used to move air through the motor to carry the heat away. An even smaller amount is used to make the humming noise that you hear.
A certain amount of energy is lost in the wire between the power supply and the motor. That could be very little if the supply is close and the wires are large. The losses between a power generation station and motors in a factory average on the order of 7%.