### Author Topic: Greetings :)  (Read 12175 times)

#### idiot94

• Sr. Member
• Posts: 484
##### Greetings :)
« on: 七月 23, 2004, 11:54:01 am »
Just drop to say hi to everyone here....

And bring a little fun problem for the friends here (very easy, just for fun, as my "jian4 mian4 li3") ... hope it makes you smile:

two bars are identical in shape, weight and otherwise appearance.
One of them is magnetic, the other is just normal iron. So when you put them close, they will attract each other. THe difference is the magnetic bar will attract other iron objects, yet, the iron bar won't.

But only given these two bars, how can you tell which is which?
In general, the men of lower intelligence won out. Afraid of of their own shortcomings ... they boldly moved into action. Their enemies, ...  thought there was no need to take by action what they could win by their brains. Thucydides, History

#### packman

• Full Member
• Posts: 226
##### Greetings :)
« Reply #1 on: 七月 23, 2004, 12:13:02 pm »
Hang them.
Oops, did I get rope besides two bars?

#### 万精油

• Hero Member
• Posts: 1831
##### Greetings :)
« Reply #2 on: 七月 23, 2004, 12:20:53 pm »
Welcome.

We need more variaties in this forum, this is a good example. I have to admit that I am not very good in solving physics related puzzles, but I still like it.

My intuition for this problem is to use the compass idea, treat the magnetic bar as the compass needle, spin it on a flat surface, and it should aways end in a fixed position, wheras the iron bar won't do this.

As for the signature, I think you may be able to set one when you register. I am not sure about it since I have never used one.  I think ascii signatures are fine, but image signatures should not be encouraged, since they create extra bandwidth problem without bringing in extra information.

#### idiot94

• Sr. Member
• Posts: 484
##### Greetings :)
« Reply #3 on: 七月 23, 2004, 12:23:20 pm »
Quote from: 万精油
Welcome.

Thanks

Quote from: 万精油

My intuition for this problem is to use the compass idea, treat the magnetic bar as the compass needle, spin it on a flat surface, and it should aways end in a fixed position, wheras the iron bar won't do this.

Good idea,.... but, ... can it be even simpler?

Quote from: 万精油

As for the signature, I think you may be able to set one when you register. I am not sure about it since I have never used one.  I think ascii signatures are fine, but image signatures should not be encouraged, since they create extra bandwidth problem without bringing in extra information.

heheh
In general, the men of lower intelligence won out. Afraid of of their own shortcomings ... they boldly moved into action. Their enemies, ...  thought there was no need to take by action what they could win by their brains. Thucydides, History

#### 差不多

• Newbie
• Posts: 10
##### Greetings :)
« Reply #4 on: 七月 23, 2004, 12:37:45 pm »
T

#### idiot94

• Sr. Member
• Posts: 484
##### Greetings :)
« Reply #5 on: 七月 23, 2004, 12:40:52 pm »
Quote from: 差不多
T

thumbs UP!

oh, I think I should briefly explain a bit --- in case some1 did not play with magnetic bars in the pencil boxes in his childhood as much as I did ...

The magnetic bar has strong magnetic field around the polar areas, however, the field is extremely weak at the middle part of the bar --- so weak that you cannot even see any significant difference from a plain iron bar. Therefore, if you use the "head" of one bar to touch the middle of the other ---- if the "head" is of the magnetic one, it will attract the iron bar (since polar field is strong); however, if it is the iron one, it will not attract the magnetic bar (since the middle field is too weak.).
You may try this by yourself .... if you have a pencil box at hand
In general, the men of lower intelligence won out. Afraid of of their own shortcomings ... they boldly moved into action. Their enemies, ...  thought there was no need to take by action what they could win by their brains. Thucydides, History