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


The following spised taken from the story of the outstanding Soviet inventor K. E. Tsiolkovsky "On the moon", will help us to understand the conditions of the movement under the action of gravity. On Earth, the atmosphere, preventing the movement of bodies, blind us to the simple laws of falling, complicating their extension. On the moon the air, missing completely. The moon would be an excellent laboratory for the study of falling bodies, if we could it to yourself and do there research.

Referring to the episode of the story, explain that two of the interlocutor the following passage are on the moon and want to explore how you will move there bullets coming from the gun.

"- But will be there to work the powder?

- Explosives in the void should manifest itself even with greater force than in the air, as the latter only prevents their expansion; as for oxygen, they are in it but need, because everything you need his number is in them.

- Install the gun vertically, to a bullet after the explosion look close...

The fire, the faint sound *, a slight concussion of the soil.

- Where is the plug? He should be here, nearby.

- Wad flew along with the bullet and hardly from behind her, so as soon as the atmosphere prevents him on Earth to keep up with the lead; here the Pooh falls and flies up with the same rapidity as the stone. Take a feather sticking out of the pillow, and I'll take the iron ball. You can throw your fluff and get it in the goal, even distant, with the same ease as I ball. I can, at low gravity, to throw a ball 400 meters; you are at the same distance can throw the fluff, however, you're nobody it doesn't kill and when throwing will not even feel that anything you throw. Let us cast our throwing projectiles struggled - which we are not very different, and in one goal: get out of the red granite...

Fluff ahead a little iron ball, as if carried along by a strong vortex.

"But what is it? With time shot three minutes passed, and no bullets?

"Wait two minutes, and it will probably come back.

Indeed, after a specified period of time, we feel a slight concussion of the soil and see Bouncing off the wad.

- How long was flying bullet! At what height it should rise?

- Seventy kilometers. This height creates low gravity and no air resistance."

Will check. If the speed of the bullet at the moment of departure from the gun barrel to take a relatively modest number of 500 meters per second (for modern rifles is one and a half times less valid), the height of lifting on Earth, in the absence of the atmosphere, would be:

i.e. 12,5 km On the moon, where the voltage of gravity is 6 times weaker, instead of g it is necessary to take 10/6 m/s2; reached by a bullet height should be equal to:

12 500 * 6 = 75 km



* The sound transmitted through the soil and bodies of the people, and not through the air, which the moon is not.

Entertaining physics J. Perelman


System Orphus


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