EfficiencyEfficiency, in science and technology, is the ratio of the work we get out of a machine to the amount of energy put into the machine. Efficiency may also be defined as the ratio of power output to the total power input. The difference between the energy put in and the work delivered often appears in the form of heat due to friction. For example, most of the electrical energy going into an electric motor is put out as mechanical energy by turning a shaft that does useful work, such as pumping water or drilling. But part of the energy given to the motor is wasted as heat in the bearings and wires. Scientists express efficiency in percentage. If a motor returns three-fourths of the energy put into it, the motor has an efficiency of 75 percent. Human beings have an efficiency of about 24 percent in converting the energy in the food we eat into mechanical energy, such as running or walking. An electrical transformer can be over 98 percent efficient.