Abstract
In my article (Featonby and Vitkoczi 2017 Phys. Educ. 52 037001) I asked what happens when a carbonated drink can is placed on a concave ramp, and is any difference observed if the can is shaken beforehand?
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A problem related to a carbonated drinks can oscillating on a concave track (figure 1) was presented. Which can oscillates the most, one which has been left still or one that has been shaken? The answer is that the shaken can makes a lot fewer oscillations. In my own test the shaken can made only half the number of oscillations (20 instead of 40).
Figure 1. The can is placed on the concave ramp.
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Standard image High-resolution imageThe pressure inside the shaken can is surprisingly the same as that in the unshaken can. This is shown in a YouTube video (www.youtube.com/watch?v=Ux29SBmnZZ4). The dissolved carbon dioxide is released into the empty space in the can and forms a covering of bubbles. So whilst the pressure inside the shaken can on the surface of the drink is not changed there are now are bubbles touching the inner surface of the can. When the can rolls the metal of the can rotates, but the liquid (and bubbles) inside do not rotate with the can....the surface stays with its midpoint parallel to the curved surface. This can be seen if a clear bottle is used (figures 2 and 3).
Figure 2. The unshaken bottle of cherryade.
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Figure 3. The shaken bottle of cherryade with bubbles.
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It is the bubbles that reduce the motion. Adhesion between the bubbles and can slows down the motion; the adhesion is much much less with liquid only.
Most of us are familiar with the problem of rolling cans down an incline. A solid cylinder for instance will roll faster than a hollow one. You can also experiment with various different contents in the cans, sand, syrup or asymmetrically placed weights.
These are the answers to the questions posed in [1].
Thanks go to Patrick Walravens (Belgium) for the initial idea.
Biographies
David Featonby retired from school physics teaching at a Newcastle comprehensive school in 2003, where he'd worked as head of physics, head of science, head of sixth form and assistant head (though not all at the same time). Most recently he has been an active member of the Science on Stage Europe executive board, helping to arrange its biannual festival and supporting on going cooperation between teachers. He continues to participate in many conferences across Europe with a variety of workshops, including 'What happens next?' based on this column.
Borbala Herendi recently qualified as a teacher from Debrecen University in Physics and French, She is a member of the Hungarian Science on Stage team.
Janos Toman works at the University of Debrecen, Hungary, in the department of Solid State Physics. He works in the field of nanoscale computer simulations and is part of the University's outreach team.