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hongqcong
member
REF: 330371
04/13/2008
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hongqcong
member
REF: 329667
04/11/2008
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Cu 2 chnh l cu 1 nhưng thay 4m bằng 3m
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hongqcong
member
REF: 329651
04/11/2008
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hongqcong
member
REF: 328250
04/08/2008
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Khng thấy g hết OTOTOT ơi
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hongqcong
member
REF: 327307
04/06/2008
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bn ny chỉ c ho thi
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hongqcong
member
REF: 325537
04/02/2008
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Đn ng = 17, 14,............, 02
Đn b = 05, 10,............, 30
Con nt = 78, 76,............, 68
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hongqcong
member
REF: 320431
03/23/2008
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Muốn thử cho đn chy sng chơi th phải biết điện thế bao nhiu volt?
AC hay DC cũng như nhau thi cng cao cng nguy hiểm.
Thn i
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hongqcong
member
REF: 316609
03/15/2008
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Why do the hands on a clock turn clockwise?
May 8, 2006
Q: I am left-handed and always frustrated by the tendency for things that have handedness to be set up for the right-handed people. It all seems so arbitrary. There is one thing that has always puzzled me, however, and that is why the hands on clocks turn ''clockwise." This also seems to be a ''handed" thing -- the fingers of my left hand naturally curl as the motion of the second hand on a clock -- but this seems to be left-handed -- a rare exception in a right-handed world. Do you have any wise thoughts to offer on this?
KS, Boston
A: You can indeed make an association between a direction of turning and the fingers of a hand, and this is often done by physicists and engineers -- but usually, no doubt to your chagrin, using the right hand for setting up conventions.
The motion of a clock hand has a different and not particularly biological origin. It is, of course, arbitrary, but the arbitrariness isn't in which hand is easier to use but in which hemisphere your ancestors with sundials were born.
Let me explain. Before we had mechanical clocks, people realized that you could keep track of time during the day by watching how shadows moved. Imagine, then, that you stand outdoors so you can see your shadow.
To do so, you must face north. To see this, you might need to look at a globe, but if you imagine standing where Boston is, you'll stick out of the earth and block the sun's rays, casting a shadow that extends from where you stand toward the north. (Had you lived in the Southern Hemisphere, things would be opposite, but let's keep the discussion fixed on the north.)
As the earth turns, your shadow will move from left to right during the course of a day. Remember, the sun rises in the east, so it will originally cast a shadow that points westward (to your left). The sun sets in the west, so it will end up casting a shadow that points to the east. The net result is that your shadow, and all the shadows you can see, move from west to east.
This was copied into the motion of the hands of a clock by clockmakers in the Northern Hemisphere and completed into a circle to cover 12 hours.
Dr. Knowledge answers your questions about science each week. E-mail questions to drknowledge@globe.com or write Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819. Include your initials and hometown. 
Copyright 2006 Globe Newspaper Company
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hongqcong
member
REF: 316361
03/15/2008
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8/
AKA lun ni dối vo ngy thứ tư, thứ 5, thứ 6 nhưng lun lun trung thực vo những ngy cn lại của tuần lễ
Trong khi đ Soluuhuong lun ni dối vo thứ 7, chủ nhật, thứ 2 nhưng lun trung thực vo những ngy cn lại của tuần lễ.
Một ngy no đ cả hai người cng ni : " Hm qua ti đ ni dối".
Theo cc bạn đ l thứ mấy trong tuần?
C phi ngy thứ 7 khng
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hongqcong
member
REF: 314648
03/11/2008
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Cu 3:
Sai chổ nầy n AKA ui
AP = PD
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hongqcong
member
REF: 307836
02/27/2008
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hongqcong
member
REF: 307832
02/27/2008
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5/
Khi niệm no dưới đy khng cng nhm?
a/ Golf
6/
dy số 1, 3, 6, 10 ?? số tiếp theo l số mấy?
15
7/
Trong 5 chữ sau đy:
Z, A, N, E, F
Chữ no khng giống 4 chữ cn lại nhất? E
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hongqcong
member
REF: 306843
02/25/2008
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Bạn muốn my mạnh cở no th nn mua tốt hơn l tự rp.
Cng ngy kỹ thuật cng cao th tự rp cng kh khăn hơn.
Tự rp c nhiều trở ngại m khng biết giải quyết th system khng chạy đươc.
Thn i
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hongqcong
member
REF: 302531
02/17/2008
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Cu 2:
? = 26
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hongqcong
member
REF: 296702
02/04/2008
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Cu 5 :
"phần lng trắng c độ dy bằng phần lng đỏ "
Cu ny khng r rng, khng c hnh vẽ, người đố muốn ni sao cũng được.
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K hiệu:
:
trang c nhn :chủ
để đ đăng
:
gởi thư
:
thay đổi bi
: kiến |
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