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


Of said right now you should not make hasty conclusion that the friction on the ice is negligible under any circumstances. Even at temperatures close to zero, the friction on the ice is often quite significantly. In connection with the operation of icebreakers carefully examined the friction of the ice of the polar seas of the steel shell of the ship. It turned out that it is unexpectedly large, not less friction iron iron: the coefficient of friction new steel ship plating on the ice equal to 0.2.

To understand what is the significance of this figure for vessels when navigating in ice, look at the picture; it represents the direction of the forces acting on the Board MN vessel when the pressure of the ice.

"Chelyuskin, jammed in the ice. Bottom: the forces acting on the MN Board the vessel when the pressure of the ice.

Power P pressure of ice is decomposed into two forces: R, perpendicular to the Board, and F, directed along the tangent to the Board. The angle between R and R equal to the angle and tilt side to the vertical. Power Q of friction of ice on Board equal to the force R, multiplied by the coefficient of friction, i.e., 0.2; we have: Q = 0,2R. If the friction force Q is less than F, the latter draws power pushing the ice into the water; ice slides along the side, not able to cause vessel damage. If the same power of Q larger F, the friction prevents the sliding of the ice, and the ice, when prolonged pressure can crush and push the Board.

When Q < F? It is easy to see that

F = R tga;

therefore, there must be inequality:

Q < R tga;

and since Q = 0,2R, then the inequality Q < F leads to another:

0,2R < R tga, or tga > of 0.2.

The tables look angle, the tangent of which is 0,2; it is equal to 11°. Hence, Q < F when a > 11°. Thus determines what the slope of the sides of the ship to the vertical provides secure sailing in ice: the slope should not be less than 11°.

Let us now turn to the death of "Chelyuskin". This ship is not an icebreaker, has successfully passed all the Northern sea route, but in the Bering Strait was trapped in ice.

Ice claimed "Chelyuskin" far to the North and crushed (February 1934). Two months heroic stay Chelyuskinites on the ice and the salvation of their heroes-pilots survived many in memory. Here is a description of the disaster:

"The sturdy metal housing is passed immediately, was announced on the radio the commander O. Y. Schmidt. - It was obvious, as the ice is pushed into the Board and as above it leaves sheathing puchatsya, curving outwards. The ice continued a slow but irresistible attack. Expanded metal sheets of the shell plating was torn along the seam. With a crash flew rivets. In an instant the port side of the ship was detached from the nose to hold the aft end of the deck..."

After what was said in this article, the reader should be clear physical cause of the accident.

This entails practical consequences: in the construction of vessels intended for navigation in ice, it is necessary to give the sides of their proper bias, namely not less than 11°.

Entertaining physics J. Perelman


System Orphus


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