Two swings

Exhibit on display in Stanislaw Lem Garden of Experiences, a branch of the Museum of Municipal Engineering in Krakow.

Description written by Olga Odziemczyk

The device consists of two connected swings. They are mounted in a wooden frame, facing each other. The frame is made of 4 pylons inclined toward one another and connected at the top with horizontal beams, and diagonally mounted support beams. The structure is rather large. The pylons are positioned in such a way that the points where they connect with the ground constitute the apexes of a rectangle measuring 9 by 3.25 meters.

Each swing hangs from the top beam, between a pair of the closest pylons. The swings are identically made of two chains hanging from the beam, with a simple seat attached at the bottom. A small distance from the seat, each chain splits in two, so that it is attached to the seat in two points. The seat is rectangular, with rounded corners.

A particularly important element of the device are two ropes that connect the upper sections of the swings’ chains. The ropes are parallel to each other and connect the chain of one swing with the corresponding chain of the other swing.

The device is designed for two people. To perform the experiment, sit on the swings. Then, one person should begin swinging, while the other person remains still, seated in the swing. Now, let both swings move freely – without moving your body or interfering with the motion of the swings. Make sure you don’t drag your feet on the ground. Focus on observing the phenomenon of transmission of vibrations. The swing of the person who sat still in the beginning will start to increase its oscillation – it will move with greater and greater amplitude. At the same time, the amplitude of the first swing will begin to decrease. After a while, the situation will reverse and the swing, whose amplitude was increasing will begin to slow down, while the other will again start increasing its amplitude. Vibrations are transmitted from one swing to the other by the ropes that connect their chains. The cycle will continue, though not indefinitely, due to friction and air resistance.

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