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[Matabiri]

I've got a spinning top I got in a Christmas cracker (yes, early, I know). When you spin it, it processes for a short while and then jumps up onto the nub you spin it by.

(If you've ever seen one of these tops, you'll know what I mean. I apologise that I haven't got a camera I can show anyone else with).

It's very cool. My theory is that, because the base is spherical, procession is a flat energy state. On the other hand, spinning on the nub is a local minimum. Hence, at some point in the procession, there's a chance it'll jump onto the nub and spin stably there.

Has anyone actually carried out an analysis on one of these tops? Can you tell me what the situation actually is?

Cheers.

 

[Matabiri]

Here's a picture, but I haven't found a video yet...

<font size=-2>Edited for repetition of "here".</font>

 

[geni]

Looks like the same idea behind getting eggs to spin on one end. I think it is something to do with angerler momentium (or maybe not).

 

[Matabiri]

Looks like the same idea behind getting eggs to spin on one end. I think it is something to do with angerler momentium (or maybe not).

Hmm... haven't tried that. I'll need to give it a go.

Of course it's got something to do with angular momentum. Everything, everywhere, has. Particularly everything cool.

 

[Iamme]

Matabiri---You mean it does a 180 degree flip, all by itself?

 

[Brown]

These tops have been analyzed by physicists. Sometimes the tops are called "Tippy Tops."

Here's a riddle: If you spin one of these tops in a clockwise direction (when viewed from above), and the top flips over, in which direction will the top be spinning?

 

[Matabiri]

Matabiri---You mean it does a 180 degree flip, all by itself?

Yup. You spin it nub-up, and it processes to nub-down.

I'd assume that, by conservation of angular momentum, the top would still be spinning clockwise when seen from above.

 

[malaka]

I've seen those before. Very cool.

Another cool "top" toy is the one that looks vaguely like a rounded wing. If you spin it one way, it will continue unfettered. However, if you spin it the other way, it will slow to a wobble...and then reverse directions!

After some searching, I found it. It's called a rattleback or celt.

 

[Iamme]

Where can you get one of these apparently nifty novelties? If I had one...then I could add it to the collection of another neat thing I have. You know how in the law of physics we know that you can't drop a bouncing ball and have it rebound higher than your dropping point? Well, there is a set of rubber balls that you drop. There are 4 or 5 balls stacked ontop each other. The bottom one is the biggest and they become smaller after that. Well, when you drop the whole grouping, big ball side down, this creates an effect similar to those steel balls that hang from strings. (You know...you let the end ball whack the other 4? balls, and the middle 3 stay where they are, and the other end ball swings outward *about* as far as what the other end-ball's travel distance was...only just not quite.) Anyway, what happens with the rubber balls...maybe you already guessed: The small ball rebounds *way* higher than the point at which you dropped the ball-grouping from.

Anything that is relatively simple, but makes you think...that has some law of physics behind it...I have always enjoyed. I also think it is kewl how you can rest a needle on top of water without the needle sinking. It's also pretty neat how you can spray Oxi-clean on a beige-white plush carpet, and the stain will completely disappear without you even touching it. Stuff like that.

 

[Brown]

Last I checked, tippy tops and rattlebacks were available at the Mall of America, which is not much help unless you happen to be in Minnesota. It is possible that places like the Discovery store have them.

Matabiri is correct, the top continues to spin clockwise after inverting itself. As Martin Gardner puts it, it becomes its own "anti-top."

As for the different-sized balls trick, you can do the same thing with a basketball and a tennis ball (some folks use a baseball), but watch out! The tennis ball (or baseball) can rocket at unexpected directions and could hurt you if it hits you.

 

[Iamme]

Thanks Brown for the basically free tip. I'll have to try that. I'll get one of the Dennis-the-Menace neighbor kids to observe. I'll say, "Dennis. Come here and watch THIS! And I will have him bend over and look as I drop the two balls together.

 

[Brown]

From Halliday, et al., "Fundamentals of Physics" (4th ed.):

[A]lign the baseball above the basketball (with a small separation as in Fig. 10-25a) and drop them simultaneously. (Be prepared to duck and guard your face.)

 

[Matabiri]

As for the different-sized balls trick, you can do the same thing with a basketball and a tennis ball (some folks use a baseball), but watch out! The tennis ball (or baseball) can rocket at unexpected directions and could hurt you if it hits you.

Safer with a table-tennis ball and tennis ball...

The important thing is the difference in mass.