Skittles Spinning Top: Exploring the Physics of Fruit-Flavoured Sweets

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In summary, the conversation discusses the shape and rotational behavior of Skittles, a type of fruit-flavored candy. The speaker mentions observing a strange property of the candy and asks for help in understanding it mathematically. They also mention observing a similar behavior in other candies such as Smarties and M&M's. The conversation ends with a humorous suggestion for further investigation and a request for a research grant.
  • #1
Cexy
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Do you get sweets called Skittles in America, or the rest of the world?

http://www.britsuperstore.com/acatalog/Skittles_Bag_55g.jpg [Broken]

We get them in the UK - they're fruit-flavoured sweets in the various colours of the rainbow. The other day, whilst savouring a pack in the cafe at the maths dept, I noticed a particularly strange property of Skittles.

Your average skittle is shaped like you chopped a section off the side of a sphere, then got two of them and stuck them together. It's kind of hard to explain, and I don't know the mathematical name for such a shape, but hopefully this picture will give you the idea:

http://www.bewarethecheese.com/skittles.jpg [Broken]

So anyway. Take a handy Skittle, put it on the table, and then spin it as fast as possible. You'll notice that it starts to wobble a bit, and then all of a sudden it flips up onto its side, so that it's spinning on its edge rather than its bottom! I imagine that this is is just because that's a more stable mode of rotation at higher speeds, but I've been unable to derive that mathematically. So if anyone could help me out, I'd be more than grateful! I'm happy as Larry with Lagrangian dynamics, so feel free to use whatever tools you have at your disposal - I just want an answer!

Ta :)
 
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  • #2
I think that the mode where it's spinning like a flying saucer should be the stable one, that's the major axis of symmetry. It should fall back down to that rotation towards the end of its movement. I would expect that if the Skittle is hopping up onto its edge and rotating about one of the minor axes of symmetry it's due to roughness of the surface or some instability in the rotation imparted during the initial spin.
 
  • #3
dicerandom said:
I think that the mode where it's spinning like a flying saucer should be the stable one, that's the major axis of symmetry. It should fall back down to that rotation towards the end of its movement.
Yeah, it does. It starts in 'flying saucer' mode, then jumps up to its edge, and then winds back down to end up lying on its belly.
I would expect that if the Skittle is hopping up onto its edge and rotating about one of the minor axes of symmetry it's due to roughness of the surface or some instability in the rotation imparted during the initial spin.
What do you mean by the 'major' axis of symmetry? The one with greatest moment of inertia?
 
  • #4
Cexy said:
What do you mean by the 'major' axis of symmetry? The one with greatest moment of inertia?

Right.

... evidently I need 10 characters ...

Edit:

I've thought about it some more, and while it's true that in this case the major axis of symmetry has the largest moment of inertia that is not true in general. I knew there was something fishy about what I'd written. The major axis of symmetry is, well, the one which is the most symmetric ;) For a cylinder, for instance, the major axis of symmetry is the one which goes straight down the middle of it. In that case it has the smallest moment of inertia.
 
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  • #5
Smarties and M & M's are the same shape. I wonder if they do it too, or if it's strictly a fruit phenomena. :uhh:
 
  • #6
Danger said:
Smarties and M & M's are the same shape. I wonder if they do it too, or if it's strictly a fruit phenomena. :uhh:
This topic certainly deserves more investigation. Research grant, anyone?
 

What is the purpose of the Skittles Spinning Top experiment?

The purpose of the Skittles Spinning Top experiment is to explore the physics of fruit-flavoured sweets. This is achieved by observing and analyzing the motion of the spinning top and its interaction with the Skittles. It also allows for a hands-on demonstration of concepts such as rotational motion, friction, and inertia.

How do Skittles affect the spinning top's motion?

Skittles affect the spinning top's motion by creating a non-uniform distribution of mass on the top, causing an imbalance in its rotation. This results in a wobbling motion and a change in the top's center of mass. Additionally, the friction between the Skittles and the surface can also impact the top's speed and direction of rotation.

What factors can influence the outcome of the experiment?

Some factors that can influence the outcome of the experiment include the size and shape of the Skittles, the type of surface the top is spinning on, and the force and angle at which the top is launched. Temperature and humidity can also affect the experiment, as they can impact the stickiness and melting of the Skittles.

What can be learned from the Skittles Spinning Top experiment?

The Skittles Spinning Top experiment allows for the application of physics principles in a fun and engaging way. By observing the motion of the spinning top and analyzing the forces at play, participants can gain a better understanding of concepts such as rotational motion, friction, and center of mass. It also highlights the importance of variables and how they can affect the outcome of an experiment.

How can the experiment be modified or expanded upon?

The experiment can be modified by using different types of fruit-flavoured sweets instead of Skittles, such as M&M's or jelly beans. It can also be expanded upon by adding multiple spinning tops and comparing their motion, or by changing the angle and force at which the top is launched. The experiment can also be used to study the effects of different surfaces, such as carpet or tile, on the spinning top's motion.

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