Site for children

J. Perelman
"Entertaining physics". Book 1.
Chapter 2. Gravity and weight. A lever. Pressure


If under certain conditions the bullet can be harmless, there is an opposite case: “peaceful body, thrown with little velocity would produce a devastating effect. During the road race Leningrad - Tiflis (in 1924) peasants Caucasian villages welcomed whizzing past them cars, throwing passengers watermelons, melons, apples. The effect of these innocent gifts were not pleasant watermelons and melons pressed, crushed and broke the back of the machine, and the apples got into the passenger, causing a serious injury. The reason is clear: own vehicle speed was with the speed of a thrown watermelon or Apple and turned them into dangerous, destructive projectiles. It is easy to calculate that the bullet 10 g has the same energy of motion as watermelon 4 kg, thrown into a car that runs with a speed of 120 km per hour. Penetration of watermelon under such conditions cannot, however, be compared with the effect of the bullet, as the watermelon does not have its hardness.

Watermelon thrown towards fast racing car, turns into a “shell”.

When you are developing a high-speed aircraft in the higher strata of the atmosphere (called the stratosphere), the aircraft will have a speed of about 3000 km per hour, i.e., the speed of bullets, the pilots have to deal with symptoms resembling considered now. Namely, every piece gets in the way of this sorbitrate aircraft will turn to him in a devastating projectile. Stumble upon a handful of bullets, just dropped from another aircraft, not even flying to still be that being fired from a machine gun: falling bullets would hit the plane with the same force with which would have struck this machine bullets from a machine gun. As the relative speed in both cases is the same (the plane and the bullet are converging at a rate of about 800 meters per second), the devastating impact of the collision will be the same.

On the contrary, if the bullet flies after the plane, rushing with equal speed, then pilot it, as we already know, harmless. The fact that a body moving with almost the same speed in the same direction, come into contact without impact, skillfully used in 1935 driver Borschev, taking the moving part of the 36 cars on your train without shock and preventing the train disaster. It happened on the South road, on the stretch of the Spruce - olszanka, under the following circumstances. In front of the train, which led Borschev, was another. Due to lack of vapor front train stopped; his cab with the steam locomotive and several cars went forward, to the station, leaving the remaining 36 cars on the road. The cars, which was not enclosed shoes, rolled downhill back with a speed of 15 km per hour, threatening to descend on the train borshcheva. Noticing the danger, resourceful engineer stopped the train and took him back, gradually developing a speed of 15 km per hour. Through this maneuver, he managed the entire 36-car train take the train without the slightest damage.

Finally, on the same principle of the instrument is extremely easy letter in a moving train. To write in the car on a moving train hard only because the shocks on the joints of the rails are transferred to the paper and the pen tip is not at the same time. If you arrange it so that the paper and the pen got a concussion at the same time, they are relative to each other will be alone and writing on the go train will have no difficulty.

This is achieved by the device shown in the figure below. Hand with pen fastened to the plate a, which is able to move in the slots on the strip b; the latter, in turn, can move in the slots of the plates lying on the table in the car. Hand, as we can see, is mobile enough to write letter by letter, line by line; however, each impulse received by the paper on the plate, in the same moment and with the same force is transmitted to the hand holding the pen. Under such conditions, the letter on the go train is becoming as comfortable as in a stationary car; prevents only that gaze on paper spurts, as head and hand get the shocks are not at the same time.

The device, which allows you to write in a moving train.

Entertaining physics J. Perelman


System Orphus


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