h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: The Squirrel Dilemna - A Puzzle - A16967659
Author: AlexAshman [!] - U566116


Quirky enough?

Alex

Yes.

I hadn't heard this one before, and I understand the maths, so it gets my vote.

I thought of another way of looking at it. If you ignore the tree, you could imagine the photographer and the squirrel at opposite ends of a rigid bar which is rotating about a point which is at the centre of the tree trunk. As this point is not necessarily at the centre of the bar, then the participants can have differing angular velocities, but their positions are fixed in relation to each other.

Icy

I'll work on adding a bit about modelling them as points on a rigid bar - that's actually such a valuable point that I'm going to offer you a credit

I understood the conclusion

I didn't even think that you would want to use it, I was just making conversation.

Please don't credit me, just include a link to Ging Gang Goolie in your next entry, or something.

Ok, I'm sorry for being too polite

I've added that bit anyway

Hi, Alex:

I'm not really questioning the validity of the entry or the maths, but I am perplexed by the term 'problem'. I'm not actually sure that you've stated the problem in terms I can understand as constituting the problem.

The first thing that occurs is that the problem is simply to get a good picture of the squirrel.

If the problem is describing the motions of the photographer and the squirrel, it seems to simply follow those of two bodies with treeo-asynchronous, concentric orbits, even if one seems more erratic and assymetrical than the other.

Certainly the photographer's wider orbit causes him/her to circumnavigate the entirety of the path taken by the squirrel. It seems that the trick would be to throw something to the opposite side of the tree to startle the squirrel into changing its location relative to the photographer and the tree.

This is a job for two photographers!

Just changing the subject line
Oh, and if it helps: my son managed to take a photo of a squirrel in Hyde Park two years ago

I look forward to reading it (I'm a bit short of time just now)

Just one preliminary remark: it should be 'dilemma', not 'dilemna'.

Excellent entry, Alex.

I actually read it + I smiled throughout = I actually understand it

I also don't think you have clearly stated the problem:

"Does the man walk around the squirrel?"

I argued this with my friends for weeks. I solved it in my head by making the squirrel walk around the tree at ground level, and then removing the tree so that the squirrel now danced around in a small circle within the large circle made by the photographer. So yes, the photographer walks around the squirrel. But my friends couldn't see it.

Tell your friends to imagine the squirrel trapped in a round cage, running around the INSIDE. When the photographer circumnavigates the cage, he will have circumnavigated whatever is inside as well.

That's all very well, but you're playing around with semantics and changing the question that's being asked. The fact of the matter is that squirrel /= tree and squirrel /= cage.

Oh and I've changed the Entry to better explain the problem posed.

Your conclusion is irrefutable, Alex, and so I'd suggest you remove the word 'simply' from "it is perfectly obvious that the photographer isn't simply orbiting the squirrel...".

I really don't understand why others seem to have a problem with this.

Icy's pole idea (which was my first thought) is surely clear enough to illustrate what is going on here.

Perhaps the following link will help to show that although the photographer (being further out from the tree) will certainly circle the path of the squirrel, he can not possibly circle the squirrel itself, since they are always facing each other:

http://www.sk8stuffmore.com/recog/p_spin_psit_bf.mpg

I've added that link.

It is so obvious that the photographer circles the squirrel that it is hard to see why it is worth writing an Entry about it.

But nevertheless some people deny that the photographer circles the squirrel. So there must be some reason why people can't see it.

I'm a bit confused.

Do you consider that the direction the squirrel is facing is important? Then it is obvious the photographer doesn't move relatively to our little furry friend: he'll just stay at given distance in the direction the squirrel is facing.

Or do you consider that the squirrel is a point (so that "facing a direction" won't make sense)? In which case I would tend to agree with Gnomon

Hmm, the way it is described, the photographer circles the tree, but not the squirrel? I'm not sure about this, though

Alex

Gnomon, in order for the photographer to circle the squirrel he must get behind it. Now, bearing in mind that the squirrel *always* positions itself directly opposite the photographer (shielded by the tree), perhaps you can tell us at what point in his circumnavigation the photographer manages to achieve this.

[If the photographer was as close to the tree (ie touching it) as the squirrel, I think you'd agree that he could not possibly circle the squirrel. Moving further from the tree makes no difference whatever since the squirrel never allows the man to get behind it.]

But, you are intitled to your view (although the maths clearly prove otherwise), and I have to say that I like you more for it

I love this. The thread exemplifies the problem perfectly, and I think Alex could do worse than to 'lift' some of the dialogue .


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