Why is it impossible to build an ideal machine?
As there are many types of losses in a machine & these losses reduces the efficiency of that machine, hence ideal machine can never be there.
For an ideal machine, its efficiency should be 100% i.e.
Output of the machine= Input of the machine.
But in practice, due to various losses & temperature effects, our output is always less than the input.
For non ideal machine, input= output + losses.