Question

write two causes to decrease the efficiency of machine

Answer 1

Simple machines: Generally friction. In engines a big loss (which is very common) is the loss of potential energy found in, say, a gallon of gasoline by all that wasted heat in the engine compartment - which is doing nothing productive. Heating a house: Any heat which goes up the chimney is a sign of inefficiency. If a tennis ball were 100% elastic it would be 100% efficient: Drop it once and it would bounce forever. But it's not perfectly elastic, the surface upon which you drop it absorbs some energy, you hear it hit the floor (sound energy... wasted energy), you know there is air friction.....