094 โ Celtic Rattleback
Reversing the direction of rotation
Introduction to:
angular momentum, conservation of angular momentum, torque.
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Material:
Celtic rattleback made of glass, available as a ready-made product
Instructions:
- Place the rattleback on a flat surface and make it rotate rapidly.
- Perform the experiment again, this time turn it in the other direction (e.g. if the first run it rotated clockwise, now make it turn anti-clockwise).
Observation:
- When spinning in one direction, the glass body retains its sense of rotation.
- When spinning in the other direction, the rotation slows down and comes to a standstill.
- A strong wobble occurs.
- Subsequently, even a rotation in the opposite direction occurs!
Explanation:
- During the wobbling, a transfer of force to the base occurs. In reaction to this, the wobble stone experiences a torque which changes its angular momentum. Conservation of angular momentum applies only to an object on which there are no acting forces.
- The total energy remains the same all the time: Initial rotational energy is transformed into kinetic and potential energy during wobbling, and then back into rotational energy.