Two swings

What can you do here
In order to perform the experiment, two people are needed.
  1. Take places on the swings. Put only only one of the swings in motion, the other one should remain static. When the amplitude of the first swing is noticeable, let them move freely. What is their behaviour?
  2. Try swinging in such a way that the swings move to the same side at the same moment – it is a symmetric oscillation.
  3. Try swinging in such a manner that the swings move to the opposite sides at the same moment – this is an antisymmetric oscillation.
How does it work
The two swings are connected with a rope and make a set of coupled pendulums. By sitting on a swing we become part of that model. When one person swings and then both let their move swings freely, we can observe the phenomenon of oscillation conveyance: so far immobile swing starts moving, reaching its highest amplitude. At the same time, the amplitude of the other swing decreases. After some time the cycle repeats. The process does not loop infinitely because of the air resistance and friction affecting the swings.

Why is this happening
Transmission of vibration is very often an undesirable effect. Especially dangerous are the oscillations of small frequencies, which are transferred to people while working with machines and devices for materials processing (drilling, crashing, grinding). The problem also pertains to communication and transport – while sitting in cars, buses, planes and trains, we have to deal with transmission of vibrations as well.