Effieciency of a machine is never 100%

in real life yes it's true because of energy lost in another way that we do not want. like car engine lost some energy as heat. So the energy from gasoline can't converted 100% to move the tire. Maybe it only 40-60 % energy use for move and the rest lost as heat and other

but sometime it can be 100% of efficiency on physics text book so that we can learn physics in the easiest way.

mistakes are ok

co2reflects heat radiation back to earth buning coal and oil emits co2 globe warms