Final answer:
Perpetual-motion machines are impossible to construct based on the first law of thermodynamics, which asserts the conservation of energy, stating that energy can be transformed but neither created nor destroyed.
Step-by-step explanation:
A perpetual-motion machine is a hypothetical concept for a machine that can operate indefinitely without an external energy source, producing more work or energy than it consumes. The pursuit for such a machine has never been successful due to the constraints of the first law of thermodynamics.
This law, also known as the law of energy conservation, states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed.
In the context of heat engines, which convert heat into work, the first law implies that the work output of an engine can never exceed the amount of heat energy input. A perpetual-motion machine would have to violate this principle, as it would essentially create energy from nothing to maintain its motion indefinitely.
Therefore, the first law of thermodynamics dictates that a perpetual-motion machine is not likely to be constructed because it would require a scenario in which energy conservation is not upheld. Energy conservation inherently forbids the possibility of a perpetual-motion device that produces more work than the energy it receives.