Site for children

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


Have you noticed what a strange feeling you have at that moment, when you begin to descend on the Elevator? Abnormal lightness, like the one experienced by the person flying into the abyss... This is nothing like the feeling of weightlessness: first movement, when the floor under your feet is already lowered, and you do not even have time to acquire the same speed, your body almost no pressure on the floor and, consequently, very little weights. A moment passes, and a strange feeling ceases; your body, trying to fall faster than a uniformly moving Elevator, presses on his floor and then again acquires its full weight.

Priveste a weight to the hook of the spring scale and watch where you move the pointer, if scales with weight quickly drop down (for convenience, place a small piece of tube into the slot of scales and note the change of its position). You will see that during the fall the pointer shows the full weight of the kettlebell, but much less! If scales fell freely and you had the opportunity during the fall to monitor their index, you would have noticed that the weight in the fall does nothing weigh: the pointer is at zero.

The heavy body is completely weightless during all that time, until it falls, it is Easy to understand why this is so. “Weight” of the body we call the force with which the body pulls the suspension point or pressure on their base. But falling body does not make any spring tension scales as the spring goes along with it. As the body falls, it has nothing to do pulls and presses. Therefore, to ask about how much the weight of the body when it falls, all the same what to ask: how much the body weighs, when it does not weigh?

Even the founder of mechanics, Galileo in the seventeenth century, wrote: “We feel a burden on our shoulders, when we try to prevent it from falling. But when we move down with the same speed as the load lying on our back, then how can he be pressing to burden us? It's like, if we wanted to hit a spear (Not letting it go. - J. P.) anyone who runs ahead of us with the same speed with which we move and we”.

The following easily enforceable experience clearly confirms the correctness of this reasoning.

The experiences that illustrate the gravity of the falling body.

One Cup of commercial scales put the tongs for cracking nuts so that one knee was resting on the Cup, another tie at the end of the thread to the hook arm. On another Cup place as much cargo, so the scales were in balance. Bring the thread lighted match; the thread will burn out and the top knee forceps will fall into the Cup.

What will happen at this point with weights? Drops if the Cup forceps at a time, until the knee is still falling, it will rise or remain in equilibrium?

Now, when you know already that a falling body has no weight, you can advance to give the correct answer to this question: the Cup must rise to the moment up.

In fact: top knee forceps, falling, although it remains in connection with the bottom, still crushes on him less than stationary. The weight of the tongs at the moment is reduced and the Cup naturally rises.

Entertaining physics J. Perelman


System Orphus



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