Why are there no machines that use energy with 100 percent efficiency?

Answer 1

From a practical standpoint there are no machines that use energy with 100% efficiency because all movement generates some friction and hence heat and loss of efficiency. Even electrons moving through superconductors generate minute amounts of heat.

From a theoretical standpoint it's impossible to get 100% efficiency; all energy transformations increase entropy. Even if you could devise a machine with no friction, the process of converting energy from one form to another ALWAYS increases entropy. It's a result of the second law of thermodynamics.

No machine can perform with 100% thermodynamic efficiency. The process used by any machine, be it steam, electric, horse drawn, wind, or whatever, can be reduced to a simple description of heat moving from a higher temperature to a lower temperature. The Carnot cycle provides a means to calculate the maximum theoretical efficiency possible. In reality, this maximum efficiency is NEVER achieved due to heat losses, friction, etc. Note that according to the Carnot cycle, 100% efficiency is impossible. The energy input to the machine can NEVER be entirely converted to useful work. Some of the energy is ALWAYS lost as heat to the surroundings.

Answer 2

It really depends on the machine. But in general, friction losses can convert useful energy to heat; the fact that a machine works at a finite speed (i.e., not infinitely slow) causes certain losses (processes that should ideally be isothermal are not - read about the Carnot cycle for more details); there can be other losses such as heat losses, eddy currents, vibrations, etc.

Answer 3

Machines always give off thermal energy. therefore they can't be 100% efficient

Answer 4

Due to losses described by the laws of thermodynamics

Answer 5

All energy transformations increase entropy

Answer 6

Some energy is usually wasted, for example, through friction, eddy currents, hysteresis in magnets, etc. This waste can be reduced, but not completely eliminated.