A perpetual motion machine of the first kind would violate the first law of thermodynamics.
The first law expresses conservation of energy: a machine cannot continuously deliver work without receiving energy or depleting an energy source. A first-kind perpetual motion machine claims to produce net work from nothing, or to create more energy than it takes in. That conflicts directly with the energy balance required for any physical process.
This classification emerged as thermodynamics clarified why ingenious-looking self-running machines fail. Medieval and early modern inventors proposed wheels, pumps, and other devices that supposedly ran indefinitely, but friction, hidden energy inputs, or stored energy always explained the apparent motion. A second-kind perpetual motion machine is a different claim: it would convert heat from a single reservoir entirely into work in a cycle, violating the second law rather than the first. Ordinary machines can run for long periods by drawing energy from fuel, sunlight, wind, or flowing water, but they are not perpetual because their external source is finite or variable.