centripetal force

piyopiyo

點解個人係個高速轉動ge盤上面會向外拋
阿sir話因為要有大ge centripetal force泥令個人有circular motion,centripetal force = mrw^2,,,r大,force大,所以個人會拋出去令r大d去做circular motion
--------
聽到我o曬嘴[[tk_30]]
centripetal force唔係泥自個盤ge friction咩,r大小影響到個friction咩
------
定係因為轉果陣個人太快,friction not high enuf,做唔到circular motion,就向外拋(due to inertia)?[[tk_24]]
定係可以用circular motion果d公式泥証明?

adamsteve

係  force黎自friction
r 影響唔到friction 但係影響到所需要ge centri. force
或者你用第二條式睇 就係 F=mv^2 / r
r愈大 要ge force愈細

至於點解會向外抛  你睇返最基本哥個圖
因為friction 只滿足到r2 (離圖心遠d ge距離) 位置ge centri. force
r1 (近d圓心) 哥個位係唔夠frictional force黎hold佢係哥度 所以佢要走

你睇返最基本哥個圖  姐係有個圓圈 有tangential 箭咀哥個圖
tangential箭咀ge出現 都係因為centri. force 岩岩好滿足左哥個"離心力"
如果太多 咁咪即係多左個力出黎  支箭咀就唔再係tangential 而係向入面走

因為每一個時刻 都要有人比人佢 引導佢跟個圓走
你諗個最盡ge case 就係0個centri. force  咁下一秒 個object ge motion咪就係真係以tangential 方向飛出去
唔係0晒 有少少ge 咪以90度以下ge角度飛出去

piyopiyo

唔係r越大,centripetal force越大咩[[tk_30]]in the case that w is constant(this case)
mv^2/r,,,但w係constant,r大左.v=rw,.,,,,v大左 ,增加ge extent仲大過r tim [[tk_30]]

[ 本帖最後由 piyopiyo 於 21-11-2008 06:09 編輯 ]

Puppet

原帖由 piyopiyo 於 21-11-2008 06:02 發表
唔係r越大,centripetal force越大咩[[tk_30]]in the case that w is constant(this case)
mv^2/r,,,但w係constant,r大左.v=rw,.,,,,v大左 ,增加ge extent仲大過r tim [[tk_30]]

Yes, you are right.

[S]【YU】

原帖由 piyopiyo 於 21-11-2008 06:02 發表
唔係r越大,centripetal force越大咩[[tk_30]]in the case that w is constant(this case)
mv^2/r,,,但w係constant,r大左.v=rw,.,,,,v大左 ,增加ge extent仲大過r tim [[tk_30]]

行行下, v 忽然大左....
really right[[tk_30]] ......乎?

piyopiyo

原帖由 [S]【YU】 於 21-11-2008 18:41 發表



行行下, v 忽然大左....
really right[[tk_30]] ......乎?

唔好理下面果句la
for the same w,r越大,需要的centripetal force越大,咁點解仲會拋出去[[tk_26]]

Zend

轉快左, 唔夠力, 走

包包 klau1001

Fc = mrw^2
for a large w,
required Fc > limiting friction
=> can't hold its circular motion
=> move in straight line (or move in a path in shape of curve due to the existence of friction ?)

piyopiyo

原帖由 包包 klau1001 於 22-11-2008 00:11 發表
Fc = mrw^2
for a large w,
required Fc > limiting friction
=> can't hold its circular motion
=> move in straight line (or move in a path in shape of curve due to the existence of friction ?)

I also think in this way[[tk_32]]

adamsteve

你睇到R愈大 F愈大 係因為你用 F =mw^2 r 哥條黎睇
無錯 e條式 你就咁睇 r大 f係會大 但係你唔好唔記得  w = v/r  w仲有square係手
所以 f同r關係 係反比  f : 1/r

正如yu神所講  w 點會係constant 呢   v(magnitude)  constant先岩
w= v/r v constant  r上升 w係下降架 唔係constant架