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J. Perelman
"Entertaining physics". Book 2.
Chapter 4. World attraction

HOW LARGE IS THE FORCE OF GRAVITY?

"If we hadn't watched every minute of falling bodies, it would have been the most amazing phenomenon," wrote the famous French astronomer Arago. The habit of doing what the attraction of all earthly objects Land seems natural and normal phenomenon. But when we say that objects attract each other, we are not inclined to believe it, because in everyday life, nothing of the sort notice.

Why, in fact, the universal law of attraction does not manifest itself constantly around us in everyday life? Why don't we see that attracted each other's tables, watermelons, people? Because for small items the force of gravity is extremely low. To cite an obvious example. Two men, separated by two meters from each other, attract each other, but the force of this attraction is negligible: for people of average weight is less than 0.01 milligram. This means that two people attract each other with such force with which the weight to within 0.00001 grams presses on a Cup of scales; only extremely sensitive scales scientific laboratories are able to detect such a small sinker! Such power is, of course, can't move us from place, this prevents friction soles of our feet on the floor. To move us, for example, on a wooden floor (friction soles on the floor equal to 30% of body weight), you need strength not less than 20 kg, it is Ridiculous to even compare this force with negligible force of attraction of one hundredth of a milligram. Milligram is a thousandth of a gram; gram - thousandth of a kilogram; mean 0, 01 mg is half of one thousandth of a share that force which is necessary to move us from one place! Is it any wonder that under normal conditions we do not notice even a hint of mutual attraction earthly bodies?

Another thing, if friction did not exist, then nothing would prevent even a weak attraction to cause the convergence of the phone But when the power of 0, 01 mg fast this convergence of people must be quite small. You can calculate that in the absence of friction, two people separated by a distance of 2 m, within the first hour has drawn near each other at 3 cm; in the next hour, they would be even closer to 9 cm; during the third hour - another 15 see Movement all accelerated, but closely two people approached would be no earlier than five hours.

The attraction of earthly bodies can be found in those cases where the friction force is no obstacle. A load attached to the thread is under the force of gravity, and so the thread has a vertical direction; but if the vicinity of the cargo is any massive body, which attracts the cargo to the thread slightly deviates from the vertical position and be sent to the resultant of gravity and the attraction of another body, relatively very weak. This deviation of the plumb near the big mountain first observed in 1775 Maskelyn in Scotland; he compared the direction of the plumb line with the direction to the pole star using the two sides of the same mountain. Subsequently, more sophisticated experiments with gravity earthly bodies using a balance of a special device made it possible to accurately measure the force of gravity.

Gravitational force between small masses is negligible. With increasing mass, it increases in proportion to their work. But a lot of people tend to exaggerate this effect. One scientist - though not a physicist, zoologist, tried to assure me that a mutual attraction, often observed between ships, called the force of gravity! It is easy to show by calculation that gravitation is not to blame: two ships of the line, 25,000 tons each, at a distance of 100 m attract each other with force 400 g of Course, this force is insufficient to inform ships in the water at least an insignificant move. The true cause of the mysterious attraction of the ships we will explain in the Chapter on the properties of fluids.


The attraction of the Sun curves the path of the Earth E.
Due to the inertia of the globe tends to rush off on a tangent line ЕR.

Negligible for small masses the gravitational force becomes very omatically when talking about the colossal masses of the heavenly bodies. So, even Neptune, very far from us planet, slowly circling almost on the edge of the solar system, send us your "Hello" the attraction of the Earth with a force of 18 million tons! Despite the huge distance that separates us from the Sun, the Earth is kept in its orbit it is only the force of gravity. If the power of the solar attraction for some reason disappeared, the Earth would fly on a line tangent to its orbit, and forever fled least in the bottomless depths of the world.

Entertaining physics J. Perelman

 




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