# Galileo and his mistakes

Who does not know the great Italian scientist of the Renaissance, by the name of Galileo? The development of mechanics in the pre-Newtonian era as a science is associated with his name. The greatest merit of Galileo as a scientist-mechanic was that he was the first to lay the foundations of scientific dynamics, which dealt a crushing blow to the dynamics of Aristotle. Galileo called dynamics "the science of motion relative to space". His essay "Conversations and mathematical proofs relating to the two new sciences" consists of three parts: the first part is devoted to uniform motion, the second part is uniformly accelerated, the third part is the forced motion of abandoned bodies. In the ancient mechanics of the term "speed" was not. Considered more or less rapid movements, as well as "equally fast", but the quantitative characteristics of these movements in the form of speed did not exist. Galileo first approached the solution of the problem of uniform and accelerated motion of massive bodies and considered the motion of bodies by inertia. But there were mistakes Galileo.

Galileo is credited with the discovery of the law of inertia. Do it even in textbooks - school and not only. Galileo expressed the law this way: "The motion of a body that is not acted upon by forces (of course, external forces) or the resultant is zero, is a uniform motion along the circumference". So, in Galileo's opinion, the heavenly bodies "provided to themselves" moved. Actually, inertia motion, as is known, can only be uniform and rectilinear. As for the celestial bodies, they are "knocked down" by this external force - the force of universal gravitation. Considering Galileo's view of inertia, we are convinced of his illegitimacy: an error in reasoning arose from the fact that Galileo did not know about the law of universal gravitation discovered later by Newton.

Proving the principle of relativity, Galileo argued that if the ship moves evenly and without pitching (Figure 1), then no mechanical experiment can detect this movement. He proposed to place in the hold of the ship the vessels with the water flowing from them, with the fish floating in them, flying flies and butterflies, and claimed that the ship was worthwhile or moving evenly - their actions did not change. Do not forget that the movement of the ship is not rectilinear, but circular (although, in the circumference of a large radius, which is a section of the Earth).

Now we know that in a system moving along a curve, which is a circle, it is impossible to observe the law of inertia: this system is not inertial. Indeed, in Galileo's principle, the magnitude of the velocity of relative motion plays no role, as does the speed of movement of one inertial system relative to the other. Here is another mistake.

But if the ship is given the first space velocity (8 km/s), then all the items in its hold, like the ship itself, will become weightless. A mechanical experiment carried out with sufficient accuracy will show that for real speeds the movement of bodies in the hold of the moving ship and the fixed ship will differ among themselves. Moreover, the movement of the bodies will change if the ship goes with the same speed, but with different courses - for example, along the meridian and along the equator. Not only the bodies moving in the hold will be strayed from the supposed trajectory, but the ship itself in the Northern Hemisphere will be referred to the right at the rate, and in the South - to the left. It is interesting that these deviations caused by the rotation of the Earth as a non-inertial system do not depend even on the direction of motion and are described by the Coriolis force.

In another of his works - "Dialogue about the two most important systems of the world..." - Galileo asserts that the world is a body of the highest perfection, and the highest and most perfect order should rule over its parts. From this Galileo concludes that the celestial bodies by their nature can not move rectilinearly, because if they moved rectilinearly, they would be irrevocably removed from their starting point and the original place for them would not be natural, and parts of the universe would not be located in "The most perfect order". Consequently, celestial bodies are inadmissible to change places, that is, to move in a straight line. The law of universal gravitation suddenly disappeared, and this would happen! It is he who keeps the celestial bodies in a steady movement, not allowing their chaotic dispersal. In addition, rectilinear motion is infinite, because the straight line is infinite, and therefore, is indefinite. Galileo believed that by the very nature of nature it is impossible for anything to move in a straight line towards an unattainable goal. Again the error of Galileo!

But as soon as the order is reached and the celestial bodies are placed in the best possible way, it is impossible for them to have a natural tendency to rectilinear movement, as a result of which they would deviate from the proper place. As Galileo argued, a straightforward movement can only "deliver material for construction", but when the latter is ready, it either remains stationary, or if it has movement, it is only circular. Moreover, Galileo argued that if the body is thrown to slide along the ice along the horizontal plane, then, falling from it, the body will necessarily cross its trajectory with the center of the Earth (Fig. 2, a). But since the inertia motion always removes the abandoned body from this trajectory, it can not cross its path with the center of the Earth in any way. This is a very common mistake that occurs even in modern textbooks!

In addition, the motion along the horizontal slippery plane is such that the body, moving away from the point of intersection of the shortest radius of the Earth with this plane, begins to move away from the center of the Earth. So, approaching, and moving away from the center of the Earth, the body can not move evenly, since all the time (except for one point in the center of the Earth) will be acted upon by force.

As we see, Galileo in his view of inertia, and, consequently, on mechanics in general, was mistaken very much. The formulation of the laws of inertia, very close to the Newtonian one and adopted with minor changes in modern mechanics, was given by the French philosopher and mathematician R. Descartes, a contemporary of Galileo. In his book "The Beginning of Philosophy", published in 1644, he thus formulates the laws of inertia. The first law: "Every thing continues, if possible, to remain in the same state and changes it only from an encounter with another." The second law: "Each material particle individually strives to continue further movement, not along a curve, but only in a straight line". Therefore, instead of calling Newton's first law, or the law of inertia, the law of Galileo-Newton, which is sometimes done in textbooks, or saying that the law of inertia was discovered earlier than Newton, it should be noted that earlier Descartes quite accurately formulated Descartes, but not Galileo. True, Galileo authority did its work and Galileo's mistakes were simply forgotten.