Why Can't a Machine Be 100 Percent Efficient?

By Staff WriterLast Updated May 27, 2020 7:41:09 PM ET
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Man and machine. Machine and man. The constant struggle to outperform each other. Man has relied on machines and their efficiency for years. So, why can’t a machine be 100 percent efficient? 

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The short answer is: It can’t. Almost all machines require energy to offset the effects of gravity, friction, and air/wind resistance. Thus, no machine can continually operate at 100 percent efficiency.

Definition of Efficiency

To get a better idea of how machine efficiency is determined, let’s look at a working definition and an example below. When speaking about electric motors, the efficiency of the system is measured by the ratio of mechanical power as it’s delivered by the motor (known as output) compared to the electrical power supplied to the motor (known as input). In a mathematical equation, efficiency equals mechanical power output divided by electrical power input x 100 percent. 

Example of Efficiency

Here’s an example of efficiency. A motorized machine utilizes 85 percent of the electrical energy input and converts it into mechanical energy. That means the motor is working at 85 percent efficiency rate, with the rest of the electrical energy transformed into heat. That’s what increases the temperature of the motor. 

Efficiency gains are made with improvements in motor design of machines. These advanced designs for machines mean less noise (think of printing machines) and less heat throughout the process. 

Most Efficient Machine

The transformer is said to be the most efficient electrical machine. The key reason behind its high efficiency is that it contains no parts of friction or resistance. In essence, there are no moving parts. That allows for more capability than other machines or electrical devices. The electrical process of mutual induction forms the efficiency concept of a transformer. 

Mutual Induction

Mutual induction occurs in transformers when other electrical components interact with another magnetic field. According to Faraday’s law of electromagnetic induction, when a conductor is exposed to a moving magnetic field, an electrical current will be induced.

This is the energy principle behind not only transformers but also motors, conductors, and generator,. Mutual induction increases a transformer’s efficiency to between 95 percent and 99 percent, making a transformer the most efficient machine. 

Common Machine Efficiency

Common machines all have to convert available energy into productive energy without a lot of waste in the process. Motors run by AC/DC electrical current with rotational energy are seen as not highly efficient, as their own power supply is needed to deal with copper losses, parts friction or wind resistance. Powering itself to resist these elements takes away its own efficiency.