CRADLE / EULER’S DISK / RATTLEBACK
Description: DEMONSTRATIONS OF NON-TRIVIAL MOTION, 2013
Artist Name: STEFAN HUTZLER
Cradle - Euler’s Disk - Rattleback presents three mechanical experiments that the audience thinks it is familiar with. However, at closer inspection, what happens it not what one thinks should happen. All three experiments continue to attract the attention of physicists and mathematicians and are regularly discussed in the specialist literature.
A Newton’s Cradle is a line of touching balls suspended from a rail by pairs of inelastic strings. In textbook illustrations it is generally claimed that displacing one ball will result in a collision that leads to another ball being ejected from the line, with all other balls remaining static. However, if one does the experiment one sees that already the first collision breaks up the line of balls. Eventually all balls move in phase. This effect is very striking if one uses large balls with a diameter exceeding 10-20cm. If a coin is spun, it first rotates and then settles rapidly.
If this ‘coin’ or Euler’s Disk is made large enough, for example 20cm in diameter, it will spin for over a minute. Furthermore, it is very noticeable that the sound created during the spinning increases in pitch as time progresses. The frequency rises very rapidly, just before the disk suddenly comes to a halt by dropping flat on the ground.
A Rattleback is a semi-ellipsoidal object that can be made to spin on its back, but only in one direction due to a slight inbuilt asymmetry of the object. This toy has been around for hundreds if not thousands of years in different cultures, and under different names, like a “celt”. The theoretical investigation into the details of the mechanism is ongoing.
Stefan Hutzler is an Associate Professor in the School of Physics, Trinity College Dublin. As a Science Gallery Leonardo he is interested in the connections between science and art. He has worked on numerous projects and exhibitions at Science Gallery and was co-curator of the BUBBLE exhibition in 2009 which explored the physics behind soap bubbles and foams.