do you find these moving?

Some perpetual motion machines and why they don't work

since as early as the 8th Century we have descriptions of 'continuously moving wheels' and other forms being experimented with. It is an aspect of science that has fascinated for centuries and it was only with the understanding of the laws of thermodynamics that we know that such machines wouldn't work, and why. All machines leech energy, and many of these are defeated by friction or equilibrium. A pure form of perpetual motion would not rely on gravity either, but as you can see, even with the assistance of gravity, none of these are successful.

I thought you'd enjoy seeing them as concepts. All the video clips are run by hidden motors.

Self flowing flask. Robert Boyle 1627-1691

Concept: the flask relies on capillary action - the means by which a tree is able to suck water upwards against gravity, - it requires a very specific size of tube to flask ratio, so that the volume of the tube is less than the volume of the flask, and the pressure from the water in the flask pushes the water in the tube up and over into the top of the flask.

Why it doesn't work: as Aristotle says, "water seeks its own level" - liquids seek equilibrium, the water would find a point where both sides contained the same pressure and stop. In reality all that would happen would be that the water would form a droplet at the top of the tube, but it wouldn't create sufficient pressure to break the surface tension and start to pour. What about a siphon? Well a siphon depends on having its output lower than its input whereas in this design the output is above the input of the tube, so using it as a siphon wouldn't work either.

1829 perpetual railway

Concept: the rail sections diverge, making the gap between them wider at the end than at the beginning, they also slant slightly uphill. A weighted wheel made from cones will climb up the slope - due to its centre of mass getting lower and lower as it rolls forward - drop to the next and continue.

Why it doesn't work: while the cones appear to be moving uphill, because the centre of the wheel is getting lower as the wheel moves forward it is in fact moving downhill, which would result in the cone requiring a lower and lower track level in order to keep moving forward, in much the same way as an ordinary wheel moves downhill. Hence this is moving downhill not uphill and will stop when it can no longer do so.

overbalanced wheel Villard de Honnecourt 1225-1250

Concept: the weights drop down as they overbalance, dragging the wheel with them. Variations on this idea go back as far as the 8th Century in India and Arabia.

Why it doesn't work: if you notice, when each hammer drops, it actually jerks the wheel backwards a fraction, meaning large amounts of kinetic energy is being lost in thermal energy and friction. Self evidently the motion could not be continued indefinitely as a result of how much is lost.

Edward Somerset, Marquis of Worcester 1601-1667 and Jacob Leupold

Concept: the weights in the rim will roll down their paths resulting in them being further away from the centre of the wheel than the balls on the other -upward- side, dragging the wheel around by their weight as they fall down.

Why it doesn't work: like the other overbalanced wheels, its aim is in fact its undoing. It's true that the further the weights are from the centre of rotational axis the greater the 'gravitational torque' is - the drag in a rotating direction on the wheel, caused by gravity on the falling balls - BUT the moment of inertia required to rotate the wheel increases with distance as well. No matter the distance of the balls from the centre, the mass needed is always proportional to the square of the radius, so as the distance from the centre gets bigger the force required to make it move also grows, meaning there is no net gain in moving the weights.

F G Woodward 1900s

Concept: the large wheel is heavier than the 2 rollers, and almost all of its weight is off-centre, to the left, forcing it to roll downwards, potentially indefinitely.

Why it doesn't work: without outside force the wheel would not begin to turn. Basically if a wheel can move equally well in either direction, you can be sure it isn't going to move in either direction on its own, it will just sit at rest. Even when initiated by an outside force, like a hand in this case, friction would eventually slow the wheel to a stop.

disclaimer: I am not a physicist, so my explanations on how these work and don't work will be a little basic, if anyone wants to add extra or more accurate information, I will happily edit in the interest of accuracy, and credit of course. Appreciation to @timgurnaregretthis for help with some of the more difficult concepts!