Experiments with invisible axes. Entertaining physical experiments at home

ENTERTAINING EXPERIENCES AT HOME
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Experiments with invisible axes. Physical experiments

Entertaining experiments in physics

Entertaining experiences at home / Physics experiments for children

The axles on which the wheels or other machine parts rotate are quite real physical bodies. You can see them, touch them. Usually these are metal shafts, rollers, rods, tubes. In railway cars, the axles rotate with the wheels, while in bicycles, for example, the wheels rotate on a fixed axle.

But the word "axis" is also used in another sense. This word is called a conditional, invisible line around which rotation occurs. A figure skater on ice performing a top, a gymnast performing somersaults in the air, and finally our planet Earth - they all revolve around invisible lines, which are called the axes of rotation. There is also such a name - the axis of free rotation. It always passes through the center of gravity of a rotating body.

We will do some experiments with such axes of free rotation. Although these axes exist, they are invisible: they cannot be seen or touched. For experiments, you need to make a device that will rotate various objects at high speed around invisible axes.

Cut out a circle with a diameter of 25-30 centimeters from thick cardboard, make a small hole in its center and place it on the round base of an old table lamp. You can replace this part with cast-iron burners from the stove or an abrasive disc for a sharpener. In a word, it must be a hard circle. If you take burners or a grinding wheel, then you will need to cut another circle from a piece of plywood of the appropriate size, make a small hole in its center and put the selected disk on this circle. A circle cut out of cardboard is placed on top. Through the middle of the resulting stack of circles (we will now call it all just a disk), thread two strong ropes and tie them at the bottom with a knot. The disk suspended from them will hang horizontally, leaning on the node.

The device is ready, let's start the experiments.

Tie a thin cord 25 centimeters long to the knot on which the disk rests. For other experiments, it may be necessary to select other laces. You can also use twine (only not paper), and for some experiments - a thin fishing line.

Tie a pencil to the end of the string hanging under the disk - at the very end. Rotating the disk, twist the ropes on which it hangs well. When you release it, it will begin to spin rapidly. A very fast rotation can be achieved by applying pressure on a round soap stick inserted between the ropes.

So, the disk is spinning. What will happen to the pencil hanging under the disk? He, too, will rotate on his cord and gradually take a horizontal position. The axis of its rotation, a free invisible axis, passes exactly through the middle of the pencil - its center of gravity.

During this and other experiments with axes of free rotation, it is necessary to adjust the speed of rotation of the disk. The speed should be sufficient to bring the suspended object to a horizontal position, but the cord should not rise to the disk itself. It is easy to achieve the desired speed of rotation by changing the degree of twisting of the ropes or the pressure on the stick inserted between the ropes.

For the next experiment, instead of a pencil, tie a circle with a diameter of about 10 centimeters, cut out of thick cardboard, to a cord. It must be tied to the very edge, making a small hole with an awl. With sufficient disk rotation speed, the circle will rotate horizontally around its free axis passing through its center.

Experiments with invisible axes

Instead of a cardboard mug, hang some symmetrical object or ring that is at hand. For example, you can hang a platter from a ski pole by the rim. When spinning fast, it will also spin horizontally.

Do another spectacular experience. Take sixteen small paper clips, chain them together to form a closed chain. Hang it under the disc on a thin fishing line. When the disk is well spun, the chain forms a ring that rotates horizontally. The invisible free axis of this ring exactly passes through its middle - its center of gravity.

Our rotating objects choose the vertical free axis themselves. For each of them, this axis turned out to be the most stable of all possible axes around which this object could rotate.

Experiments with invisible axes

Making the experiments described here, try to change the length of the cord for hanging objects, the place where the cord is attached. The disk should hang strictly horizontally, not sway. Of course, as in all other experiments, one must always exercise patience and perseverance.

An interesting experiment with free rotation is described in "Mechanics" by S. P. Strelkov.

Experiments with invisible axes

A matchbox has three mutually perpendicular axes of free rotation passing through its center of gravity. But it has only two most stable axes of rotation: one passes vertically through the middle of the matchbox, and the other runs horizontally along the box. And the axis that runs across the box does not provide stable rotation. Grab an empty matchbox with two fingers and flip it up with a flick of your other hand. Do this several times, each time making the box rotate alternately around one of the three axes mentioned above. Look carefully, and you will see for yourself which of the three axes the box rotates better, more clearly.

Author: Rabiza F.V.

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