Among the many projects of "perpetual motion" there were many of them, which are based on floating bodies in the water. High tower, 20 m in height, filled with water. At the top and bottom of the tower pulleys, over which hung a durable rope in the form of an endless belt. The rope attached 14 hollow cubic meter boxes in height, consisting of iron sheets so that the inside of the drawers of water cannot penetrate. Our risda represent the appearance of a tower and its longitudinal section.

The project imaginary "eternal" the water engine.

The device of the tower of the previous figure.
How does this install? Everyone is familiar with the law of Archimedes, realize that the boxes being in the water will tend to float up. Them draws upward force equal to the weight of the water displaced by the boxes, i.e., the weight of one cubic meter of water, repeated as many times as boxes submerged in water. Seen from the figures that the water is always six boxes. Then the power, enthralling shipped the boxes up, equal to the weight of 6 m^{3} of water, i.e. 6 tonnes. Down them pulls their own weight boxes, which, however, is balanced by the load of the six boxes, loose-hanging on the outside of the rope.

So, rope, thrown this way will always be susceptible to the pull of 6 tons, applied to one side and upward. It is clear that this force will cause the rope continuously rotating, slipping on the pulleys, and at each turn to do the work in 6000 * 20 = 120 000 KGM.

Now it is clear that if you cover the country such towers, we will be able to receive infinite amount of work sufficient to cover all needs of the national economy. The tower will rotate the armature dynamos and give electrical energy in any amount.

However, if you look closely in this project, it is easy to verify that the expected motion of the rope to happen does not happen.

To the endless rope is rotated, the boxes should enter the water tower from the bottom and leave the top. But, coming into the pool, the mailbox must overcome the pressure of a column of water 20 m tall! This pressure per square meter square box is no less than twenty tons (weight 20 m^{3} of water). The pull up is only 6 tons, i.e. not significant enough to drag a box in the pool.

Among the many samples of water "eternal" engines, hundreds of which were invented by the inventors of the losers, you can find a very simple and ingenious ways.

Look at the picture. Part of the wooden drum, mounted on the axis, all the while immersed in water. If the fair Archimedes law, the submerged part should pop up and as soon as the pushing force is more friction on the axis of the drum, the rotation will never stop...

Another project "eternal" the water engine.
Do not rush to build this "eternal" engine! You certainly will fail: the drum will not budge. What's the matter, what is the error of our reasoning? It turns out that we did not consider the direction of the acting forces. As directed, they will always be perpendicular to the drum surface, i.e. along the radius to the axis. From everyday experience, everyone knows that it is impossible to force the wheel to rotate, putting efforts along the radius of the wheel. To cause rotation, it is necessary to apply the force perpendicular to the radius, i.e., tangent to the circumference of the wheel. Now it is easy to understand why in this case fails to attempt a "perpetual" motion.

The law of Archimedes gave a seductive food for thought seekers "eternal" engine and encouraged to come up with clever features for the apparent loss of weight in order to obtain eternal source of mechanical energy.