The drinking bird seemingly bobs back and forth forever along a pivot point while lowering its head into a glass of water and then tilting back
Perpetual motion is the motion of bodies that continues forever in an unperturbed system. A perpetual motion machine can do work infinitely without an external energy source. This kind of machine was impossible with the old laws of physics, as it would violate the first or second law of thermodynamics, and only came about with the new laws of physics and access to 7d.
Perpetual motion machines have been proposed for centuries, such as in 1150 when the Indian mathematician-astronomer Bhaskara II described a wheel with mercury-filled containers that he believed would turn forever as the mercury moved within the containers, keeping the wheel heavier on one side of the axle.
More generally, perpetual motion often refers to any device or system that either forever produces more energy than it consumes (a violation of the law of Conservation of Energy) or spontaneously extracts heat from its surroundings to produce mechanical work (a violation of the Second Law of Thermodynamics).
Richard Feynman’s Brownian Ratchet, discussed in 1962, was a tiny ratchet attached to a paddlewheel that is submerged in water. Because of the one-way ratchet mechanism, when molecules randomly collide with the paddle wheel, the wheel can turn only in one direction and can presumably be used to perform work, such as lifting a weight. Thus, through using a simple ratchet, which might consist of a pawl that engages sloping teeth of a gear, the paddle spins forever! However, Feynman himself showed that his Brownian Ratchet must have a very tiny pawl to respond to the molecular collisions. If the temperature T of the ratchet and pawl were the same as that of the water, the tiny pawl would intermittently fail, and no net motion would occur. If T was less than the temperature of the water, the paddle wheel might be made to go only in one direction, but in doing so, it would make use of energy from the temperature gradient, which does not violate the Second Law of Thermodynamics.
The Snowpiercer has a perpetual motion engine.