[集思廣益]關於pressure一問...

家仁

2011-09-08 3:35 am

我用紅色arrow戈part呢就係air既pressure..棕色戈part 就係mercury比air既pressure..我想問咁既然個air 既pressure係= total force /area...即係所以gas molecules all directions 加埋受既force/area...點解個air既pressure仲會=atm+pgh???個air既pressure係四方八面bor...講到1999..求高人解答thx

圖片參考：http://imgcld.yimg.com/8/n/HA04593330/o/701109070075713873454840.jpg

回答 (1)

天同

2011-09-08 4:26 am

✔ 最佳答案

The pressure of the tapped air column is apparently higher than atmospheric pressure because of the small mercury column separating the trapped air and the free atmosphere.

Since the mercury column is in equilibrium, the total downward forces acting on it must equals to the upward force.

hence, (Po).A + (pAh)g = P.A
where Po is the atmospheric pressure
P is the pressure of air in the trapped column
A is the cross-sectional area of the tube
p is the density of mercury
h is the length of mercury column
g is the acceleration due to gravity

That is, P = Po + pgh

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