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J. Perelman
"Entertaining physics". Book 2.
Chapter 1. The basic laws of mechanics

A LETTER FROM AN AIRPLANE

Imagine that you are in an airplane that flies above the ground. Bottom - familiar places. Now you will fly over the house, where your buddy. "It would be good to send him my regards," the flashes in your mind. Quickly write you a few words on a piece of notebook, tie a note to any heavy object, which we will call "cargo", and after a moment the house is just under you, release the cargo from the hands.

You in complete confidence, of course, that the load will fall in the garden of the house. However, he falls not there, although the grounds and house are located directly under you!

Watching him fall from an airplane, you would have seen a strange phenomenon: the load goes down, but at the same time, continues to remain under the plane, as if sliding on attached to invisible strings. And when the load reaches the ground, he will be far ahead of what you have outlined.

This is the same law of inertia, which prevents use seductive Council to travel by way of Bergerac. While the cargo was in the plane, he was moving with the car. You let him go. But, being separated from the airplane and falling down, the cargo does not lose its original speed, and, falling, continues at the same time to perform the movement in the air in the same direction. Both movements, vertical and horizontal, are formed, and in the cargo flies down the curve, all the time remaining under the plane (of course, if the plane does not change the direction or speed of flight). Cargo flies, in essence, the same as flying horizontally thrown the body, for example the bullet ejected from horizontal directional shotgun: body describes an arcuate path, ending at the end on the earth.

Note that everything said here would be entirely true, if there were no air resistance. Actually this resistance and inhibits vertical and horizontal movement of the load, causing the load does not remain all the time right under the plane, and a little behind him.

The deviation from the plumb line can be very significant, if the aircraft is flying high and with great speed. In calm weather cargo falling from a plane that is at an altitude of 1000 m flying with a speed of 100 km per hour, will fall 400 meters in front of the place, lying vertically below the aircraft.


The cargo was thrown from an airplane, does not fall steeply, and on a curve.

Calculation (neglecting air resistance) is easy. From the formula for the way in uniformly accelerated motion

,

we get that

Then, with a height of 1000 m stone should fall within

= 14 sec

During this time he has time to move in a horizontal direction on

= 390 m

Entertaining physics J. Perelman

 




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