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J. Perelman
"Entertaining physics". Book 2.
Chapter 2. Power. Work. Friction


The story of "Swan, cancer Yes pike to carry with Luggage who took"known. But hardly anyone tried to consider this story from the point of view of mechanics. The result is not similar to the conclusion fabulist Krylov.

Before us is a mechanical problem on the addition of several forces acting at an angle one to the other. The direction of the forces defined in the fable:

... Swan breaks in the clouds,
Cancer moves back and pike pulls into the water.

This means (see Fig.), that one force, thrust Swan, directed upwards; the other, bent pike (S), - sideways; the third, traction cancer (OS), is back. Let us not forget that there is a fourth force is the weight of the who, which is directed vertically downwards. The fable claims that "nowhere", in other words, that the resultant of all applied to the who forces is zero.

The problem of krylovskij Swan, cancer and pike, is solved according to the rules of mechanics.
The resultant (OD) should captivate the who into the river.

Is this true? 'll see. Swan, rushing to the cloud, does not interfere with cancer and pike, even helps them: pull Swan, directed against gravity, reduces the friction of the wheels on the ground and about the axis, making the weight of who, and maybe even quite a balancing it, because the load is small ("load would be for them and seemed easy"). Assuming for simplicity the latter case, we see that there remain only two forces: thrust cancer and thrust of a pike. The direction of these forces States that "cancer is walking backwards, and pike pulls in the water." Needless to say that the water was not ahead of who, and somewhere on the side (not to sink the same who gathered Krylovskiy workers!). Hence, the strength of cancer and pike angled one to the other. If the applied forces are not collinear, then the resultant of them cannot be equal to zero.

Acting in accordance with the rules of mechanics, building both strength S and OS parallelogram, the diagonal of its OD gives the direction and magnitude of the resultant. It is clear that this resultant force must move the who, the more weight that is completely or partially balanced by the thrust of a Swan. Another question is in which direction will move the who: forward, backward, or sideways? It depends upon the correlation of forces and the magnitude of the angle between them.

Readers, have some practice in the composition and decomposition of forces, can easily understand and in that case, when the power of the Swan does not equate weight of the who; they will make sure that who and then cannot remain stationary. Only one condition who may not be moved under the action of three forces: if the friction at its axis and about the roadway is greater than the effort. But this is not consistent with the assertion that "the load would be for them and seemed easy".

Anyway, the wings could not say with certainty that "all who no go"that "nowhere". This, however, does not change the meaning of the fable.

Entertaining physics J. Perelman


System Orphus


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