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標題: [學術探討] 物理求教 [打印本頁]

作者: 小小羊仔 時間: 2011-9-27 19:26 標題: 物理求教

嘛...其實也只是一個問題
就是想知velocity跟speed的分別

作者: 仁一個 時間: 2011-9-27 19:28

velocity→要把方向納入計算

speed→不用

假設Take right hand side as the positive side
向左走的velocity就會是負數

作者: 0083 時間: 2011-9-27 19:29 標題: 轉

Just as distance and displacement have distinctly different meanings (despite their similarities), so do speed and velocity. Speed is a scalar quantity that refers to "how fast an object is moving." Speed can be thought of as the rate at which an object covers distance. A fast-moving object has a high speed and covers a relatively large distance in a short amount of time. Contrast this to a slow-moving object that has a low speed; it covers a relatively small amount of distance in the same amount of time. An object with no movement at all has a zero speed.

Velocity is a vector quantity that refers to "the rate at which an object changes its position." Imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. While this might result in a frenzy of activity, it would result in a zero velocity. Because the person always returns to the original position, the motion would never result in a change in position. Since velocity is defined as the rate at which the position changes, this motion results in zero velocity. If a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. Every step must go into moving that person further from where he or she started. For certain, the person should never change directions and begin to return to the starting position.

Velocity is a vector quantity. As such, velocity is direction aware. When evaluating the velocity of an object, one must keep track of direction. It would not be enough to say that an object has a velocity of 55 mi/hr. One must include direction information in order to fully describe the velocity of the object. For instance, you must describe an object's velocity as being 55 mi/hr, east. This is one of the essential differences between speed and velocity. Speed is a scalar quantity and does not keep track of direction; velocity is a vector quantity and is direction aware.

The task of describing the direction of the velocity vector is easy. The direction of the velocity vector is simply the same as the direction that an object is moving. It would not matter whether the object is speeding up or slowing down. If an object is moving rightwards, then its velocity is described as being rightwards. If an object is moving downwards, then its velocity is described as being downwards. So an airplane moving towards the west with a speed of 300 mi/hr has a velocity of 300 mi/hr, west. Note that speed has no direction (it is a scalar) and the velocity at any instant is simply the speed value with a direction.

As an object moves, it often undergoes changes in speed. For example, during an average trip to school, there are many changes in speed. Rather than the speed-o-meter maintaining a steady reading, the needle constantly moves up and down to reflect the stopping and starting and the accelerating and decelerating. One instant, the car may be moving at 50 mi/hr and another instant, it might be stopped (i.e., 0 mi/hr). Yet during the trip to school the person might average 32 mi/hr. The average speed during an entire motion can be thought of as the average of all speedometer readings. If the speedometer readings could be collected at 1-second intervals (or 0.1-second intervals or ... ) and then averaged together, the average speed could be determined. Now that would be a lot of work. And fortunately, there is a shortcut. Read on.

作者: 小小羊仔 時間: 2011-9-27 19:30

QUOTE:

原帖由 仁一個 於 2011-9-27 19:28 發表
velocity→要把方向納入計算

speed→不用

假設Take right hand side as the positive side
向左走的velocity就會是負數

3Q 幫大忙了
另外一個問題要是老師教得很不明白(不止我一個人) 想自學的話有什麼好方法介紹嗎?

QUOTE:

原帖由 0083 於 2011-9-27 19:29 發表
Just as distance and displacement have distinctly different meanings (despite their similarities), so do speed and velocity. Speed is a scalar quantity that refers to "how fast an object is ...

C+V也好歹先做一下整理看得眼睛痛啊..

[ 本帖最後由小小羊仔於 2011-9-27 19:45 編輯 ]

作者: UniCorn 時間: 2011-9-27 19:44

QUOTE:

原帖由 0083 於 2011-9-27 07:29 PM 發表
Just as distance and displacement have distinctly different meanings (despite their similarities), so do speed and velocity. Speed is a scalar quantity that refers to "how fast an object is ...

唔識就咪 quote 啦...
解釋velocity跟speed的分別使乜咁大推廢話
只需vector跟scaler兩個字

作者: 小小羊仔 時間: 2011-9-27 19:48

QUOTE:

原帖由 UniCorn 於 2011-9-27 19:44 發表

唔識就咪 quote 啦...
解釋velocity跟speed的分別使乜咁大推廢話
只需vector跟scaler兩個字

你只說那二個字大約我會一輩子都不明白(?)

作者: UniCorn 時間: 2011-9-27 19:54

所有Physics 書都是這樣教的吧...

Vector(manitude+direction)    scaler(manitude)
displacement                         distance
velocity                                  speed
acceleration
jerk

作者: kimwong3252000 時間: 2011-9-27 20:24

velocity--係Force and Motion會常用

speed--係physics speed甚少用

velocity係要計方向, 而且只係計由起點到終點既直線距離

speed就相反

作者: UniCorn 時間: 2011-9-27 20:56

QUOTE:

原帖由 kimwong3252000 於 2011-9-27 08:24 PM 發表
speed--係physics speed甚少用

speed 喺circular motion 經常用

QUOTE:

原帖由 kimwong3252000 於 2011-9-27 08:24 PM 發表
velocity係要計方向, 而且只係計由起點到終點既直線距離

speed就相反

那是 displacement 吧 = =
仲有唔係相反...
speed 同 velocity 嘅分別只在於有冇方向

作者: 小小羊仔 時間: 2011-9-27 21:00

QUOTE:

原帖由 小小羊仔 於 2011-9-27 19:30 發表

另外一個問題要是老師教得很不明白(不止我一個人) 想自學的話有什麼好方法介紹嗎?

我表示這一句被人完全無視啊?

作者: 真田 時間: 2011-9-27 21:09 標題: 回復 #10 小小羊仔的帖子

補習, 補ken chan

作者: UniCorn 時間: 2011-9-27 21:12

QUOTE:

原帖由 小小羊仔 於 2011-9-27 09:00 PM 發表

我表示這一句被人完全無視啊?

為何要編輯而不在#6問 - -

QUOTE:

原帖由 小小羊仔 於 2011-9-27 07:30 PM 發表
另外一個問題要是老師教得很不明白(不止我一個人) 想自學的話有什麼好方法介紹嗎?

1.落左堂問到明為止
2.問其他教得好嘅老師
3.補習社

不明白便問啊,一定要自學嗎?你可是交了學費的

除非你是愛因斯坦或霍金,否則不建議自學

作者: 小小羊仔 時間: 2011-9-27 21:12

QUOTE:

原帖由真田於 2011-9-27 21:09 發表
補習, 補ken chan

補習就能學會我去學校幹嘛?

>1.落左堂問到明為止
2.問其他教得好嘅老師
3.補習社

不明白便問啊,一定要自學嗎?你可是交了學費的

除非你是愛因斯坦或霍金,否則不建議自學 [/quote]

我表示落堂再問多久我還是不明白(攤手
本來有一位教得不錯的卻在今年走了(默
第3點同上不解釋

[ 本帖最後由小小羊仔於 2011-9-27 21:14 編輯 ]

作者: 真田 時間: 2011-9-27 21:14 標題: 回復 #13 小小羊仔的帖子

我當初都咁諗
但遲下你就會想補=]

作者: UniCorn 時間: 2011-9-27 21:15

QUOTE:

原帖由真田於 2011-9-27 09:09 PM 發表
補習, 補ken chan

55,Ken Chan 在補習界中是比較不 exam oriented 的

作者: 小小羊仔 時間: 2011-9-27 21:18

QUOTE:

原帖由 UniCorn 於 2011-9-27 21:15 發表

55,Ken Chan 在補習界中是比較不 exam oriented 的

老爸表示 : 我沒那種錢

作者: 真田 時間: 2011-9-27 21:18

我唔知你間學校教成點啦
但如果你連velocity同speed都分唔到既話
真係建議你趁仲有3年時間去補習打好個底=]

作者: 真田 時間: 2011-9-27 21:19 標題: 回復 #16 小小羊仔的帖子

依啲錢唔慳得
如果唔係到時讀asso仲貴啦,係咪?

作者: 真田 時間: 2011-9-27 21:20 標題: 回復 #15 UniCorn 的帖子

好可惜我中六中期先跟佢

作者: 小小羊仔 時間: 2011-9-27 21:20

QUOTE:

原帖由真田於 2011-9-27 21:18 發表
我唔知你間學校教成點啦
但如果你連velocity同speed都分唔到既話
真係建議你趁仲有3年時間去補習打好個底=]

不是學校問題是老師問題(攤手)
那老師可是歷代師兄都建議我去先找補習比較好(默)
...可惡!我果然不該選這科了嗎(反桌)

作者: UniCorn 時間: 2011-9-27 21:21

QUOTE:

原帖由 小小羊仔 於 2011-9-27 09:12 PM 發表

補習就能學會我去學校幹嘛?

就是因為你去學校學不會才要去補習啊...
學校就能學會我去補習幹嘛 zzz

(我只在中六補過 Physics...
那年 Physics 老師中風了,學校臨時請了個返黎...質素可想而知)

[ 本帖最後由 UniCorn 於 2011-9-27 21:27 編輯 ]

作者: 真田 時間: 2011-9-27 21:23 標題: 回復 #20 小小羊仔的帖子

physics其實算最易考
(比起bio, chem)
至少肯努力會野睇下
但chem同bio呢...

作者: 真田 時間: 2011-9-27 21:25 標題: 回復 #21 UniCorn 的帖子

我果個虧到仆街
今年有兩條友a左就以為自己教得好好[sosad]
跟本係啲人本身勁

作者: 小小羊仔 時間: 2011-9-27 21:28

QUOTE:

原帖由真田於 2011-9-27 21:23 發表
physics其實算最易考
(比起bio, chem)
至少肯努力會野睇下
但chem同bio呢...

認為bio比phy容易的我是怎麼回事(默)
不過還是認為phy比較想入就選phy了

作者: UniCorn 時間: 2011-9-27 21:29

QUOTE:

原帖由真田於 2011-9-27 09:23 PM 發表
physics其實算最易考
(比起bio, chem)
至少肯努力會野睇下
但chem同bio呢...

我覺得 Chem 易過 Physics...
(興趣問題?

作者: 真田 時間: 2011-9-27 21:31 標題: 回復 #24 小小羊仔的帖子

讀咪易囉, 考果陣你就知驚

作者: 真田 時間: 2011-9-27 21:31 標題: 回復 #25 UniCorn 的帖子

chem我覺得努力同收穫唔成正比

作者: 小小羊仔 時間: 2011-9-27 21:34

QUOTE:

原帖由真田於 2011-9-27 21:31 發表
讀咪易囉, 考果陣你就知驚

我連bio考出來的分數都比phy高耶(默
不過對bio不感興趣

[ 本帖最後由小小羊仔於 2011-9-27 21:36 編輯 ]

作者: kimwong3252000 時間: 2011-9-27 21:37

QUOTE:

原帖由 小小羊仔 於 2011-9-27 21:34 發表

我連bio考出來的分數都比phy高耶(默
不過對bio不感積趣

我phy-->bio-->chem

physics感覺上最易, 因為背熟幾條式基本上可以答到>70%問題

bio一咪靠背, 只要死背既話, 答哂全部問題都無問題

chem就要活學活用, 透過書中既example再轉一轉個問題

作者: 真田 時間: 2011-9-27 21:37 標題: 回復 #28 小小羊仔的帖子

校內試唔準架!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
記住唔好信, 一信就瀨野

作者: kimwong3252000 時間: 2011-9-27 21:38

QUOTE:

原帖由真田於 2011-9-27 21:37 發表
校內試唔準�
記住唔好信, 一信就瀨野

我考校內一定可信

因為.....

我地既marking scheme係跟AL (倒

我靠DSE也不用跟AL的marking scheme, 我要那麼高要求幹啥- -?

作者: UniCorn 時間: 2011-9-27 21:40

QUOTE:

原帖由真田於 2011-9-27 09:31 PM 發表
chem我覺得努力同收穫唔成正比

對沒興趣的科目不會付出努力
對有興趣的科目不會計較收穫

作者: 小小羊仔 時間: 2011-9-27 21:42

所以找補習以外別無他法只能打破沙盤問到督嗎?(有錯字?)

作者: UniCorn 時間: 2011-9-27 21:43

QUOTE:

原帖由真田於 2011-9-27 09:37 PM 發表
校內試唔準�
記住唔好信, 一信就瀨野

絕對認同

中化mock 5 5 4 4 3
AL 5 4 3 1 1
仲要 1左文化同實用文 = =
搞到得E

作者: 0083 時間: 2011-9-27 21:46

收啦,乜都唔知就係度亂講

作者: 小小羊仔 時間: 2011-9-27 21:48

QUOTE:

原帖由 0083 於 2011-9-27 21:46 發表
收啦,乜都唔知就係度亂講

那是你吧

作者: 0083 時間: 2011-9-27 21:49

收啦,乜都唔知就係度亂講

作者: UniCorn 時間: 2011-9-27 21:51

(看日期)未到29號啊?

作者: gary1112 時間: 2011-9-27 21:52 標題: 回復 #38 UniCorn 的帖子

佢ge生理時鐘快左n倍...........

作者: 0083 時間: 2011-9-27 21:53

收啦,乜都唔知就係度亂講(俾人發現左,提前

作者: 小小羊仔 時間: 2011-9-27 21:55

QUOTE:

原帖由 0083 於 2011-9-27 21:53 發表
收啦,乜都唔知就係度亂講(俾人發現左,提前

你不要連我認真研究學業的時候也來搞事好不好?
上一次我都不再理你了這一次你又為了什麼來搞事啊?
很空?中二病嗎?

作者: 0083 時間: 2011-9-27 21:55 標題: 回復 #41 小小羊仔的帖子

收啦,乜都唔知就係度亂講(很空

作者: 小小羊仔 時間: 2011-9-27 21:57

那傢伙終於被禁了嗎...?

作者: 仁一個 時間: 2011-9-27 22:08

唔...俺什麼也還沒做啊zzz

作者: kimwong3252000 時間: 2011-9-27 22:10

QUOTE:

原帖由 仁一個 於 2011-9-27 22:08 發表
唔...俺什麼也還沒做啊zzz

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