Tricks with cord or twine. Effective trick and its solution

EFFECTIVE FOCUSES AND THEIR CLUES
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Tricks with cord or twine. Focus Secret

Spectacular tricks and their clues

Directory / Spectacular tricks and their clues

Focus Description:

The performer lays out the cord on the table in an intricate way, and the spectator tries to put his finger inside one of the loops formed so that it is caught when the magician begins to pull the cord off the table. There are many ingenious ways of laying the cord that allow the magician to be the master of this game, i.e., either to grab the spectator's finger or leave it free, no matter where the spectator places it. On fig. 25 shows the simplest version with two loops. Regardless of which of them, A or B, the viewer chooses, the showman can let him win or lose by collecting the ends of the cord in one way or another.

On fig. 25 these two methods are indicated respectively by arrows C and D.

Tricks with cord or twine
Ris.25

This trick is also conveniently shown with the help of a belt, which is first folded in half, and then twisted into a spiral around the thumb and forefinger (one of which is first inserted into the loop). The viewer usually tries to follow the loop into which the pointing finger was first placed. However, no matter where the viewer then puts his finger, believing that he puts it in a loop, the demonstrator can pull off the belt without hindrance. Here, as in the case of the cord, the demonstrator, at will, can either freely pull the belt from the finger, or leave the finger captured.

To show another entertaining trick, you need a cord and twine at least 6 m long. The ends of this cord are tied in a knot to make a closed curve, and someone from those present is asked to lay the cord on the carpet so that an arbitrarily complex pattern is formed (Fig. 26) , but with the condition that it does not have self-intersections.

Tricks with cord or twine
Ris.26

Then newspapers are laid along the edges of the pattern, so that only its inner rectangular part remains visible (Fig. 27).

Tricks with cord or twine
Ris.27

Now the spectator places his finger and holds it pressed anywhere in the pattern. The question is: if one of the newspapers is removed and some part of the cord that was under the newspaper is pulled outward, will the spectator's finger be caught in the cord, or will it remain free? Considering the complexity of the pattern, as well as the fact that the borders hide it! under the newspaper, it seems quite impossible to guess which places on the carpet will be internal in relation to the closed curve indicated by the cord, and which external. Nevertheless, every time the pointer can accurately determine whether the finger will be captured by the hole or not.

Another version of this puzzle requires a dozen or more simple pins. Showing quickly and, as it seems, quite at random, places them in various places in the visible part of the pattern, until the entire rectangle is studded with them. Then the cord is pulled off the carpet and all the pins remain free. You can take one pin, different in color (or size) from the rest, and place it on the pattern so that after pulling the cord from the carpet, it will remain the only one caught in the loop, while all the others will be free. One more option can be proposed, when all the pins are placed inside a closed curve. In this case, the cord to be tightened forms a loop surrounding all the pins.

All these puzzles are based on a few simple rules. If any two points lie inside the curve formed by the cord, then an imaginary line connecting them intersects this curve an even number of times. The same is true in the case when both points lie outside the curve. But if one point lies inside and the other outside the curve, then the connecting line always gives an odd number of intersections.

Before the newspapers are placed, mentally select on the pattern near its middle some point external to the curve. This is easy to do by drawing, for example, an imaginary line from some point outside the pattern towards the middle. You can, for example, remember point A in fig. 27. Now, even with the borders of the pattern covered with newspapers, it will not be difficult for you to determine whether the point of interest to you will be internal or external.

To do this, you just need to draw an imaginary line (it does not have to be a straight line, although, of course, a straight line is the easiest to imagine) from the desired location to a point that you know is external, and note whether the number of intersections will be even or odd.

The method for demonstrating all the options described above is simple. A dozen pins can be quickly placed outside a closed curve as follows. Stick the first pin in a predetermined place, then cross the curve twice and stick the next one, cross the curve twice again and stick the third pin, etc. If you want to grab any one marked pin, then before sticking it into the carpet , cross the curve once, starting from any pin already stuck. Of course, you can just as quickly stick all the pins inside a closed curve.

A similar trick can be shown with a pencil and paper. Ask someone to draw an arbitrarily complex closed curve on paper (without self-intersections, of course) and fold back all four sides of the sheet so that only the inner rectangular part remains visible (Fig. 28).

Tricks with cord or twine
Ris.28

Let the viewer, next, put a few crosses on the pattern. You take a pencil and, without thinking, trace a series of crosses, saying that they all lie inside the curve. After that, the sides of the sheet are folded back and everyone can check that you are not mistaken.

Author: M.Gardner

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