If the opening is not a hole on the water tank

送交者: gyro 于 2010-01-04, 12:49:26:

回答: “自来水流过较小管径时的压力变化”的问题由 lightman 于 2010-01-04, 11:45:23:

but is connected to a long (horizontal) hose, then the flow speed will dimish, even eventually diminishes to zero as the hose is extended.

If the wall of the tank is of finite thickness, and the opening radius is smaller than the wall thickness, then the hole is like a hose. The speed of the out flow depends on the hole size.

This is because there is some friction within the water.

所有跟贴:

接一根短的管子，摩擦可以忽略不计。捏扁管子的时候水的速度会不会变大？ - lightman (24 bytes) 2010-01-04, 13:05:57 (400977)
- 那个速度只是最细地方的，如果水束比最细的地方粗，就慢了 - AQuestion (73 bytes) 2010-01-04, 15:02:59 (401022)

加跟贴

bozzle-->nozzle (无内容) - gyro (0 bytes) 2010-01-04, 13:16:48 (400993)

如果摩擦可以忽略不计－管子无流阻. (无内容) - DW (0 bytes) 2010-01-04, 13:49:42 (401009)

Then the speed will be the same - gyro (297 bytes) 2010-01-04, 14:00:31 (401012)
- 经验似乎是：堵住管子速度会变大。你的意思是这必须用粘性来解释？ - lightman (40 bytes) 2010-01-04, 14:13:59 (401015)
  - I assumed friction when I talked about pressure drop - gyro (66 bytes) 2010-01-04, 14:43:53 (401019)
    - 这个快慢是因为在水管路上有比出口小的口径比如龙头开关。摩擦力不是关键 - AQuestion (162 bytes) 2010-01-04, 18:33:46 (401066)
      - 靠捏扁管子出口使流速增加好多倍是可以的 - gyro (90 bytes) 2010-01-04, 19:46:43 (401081)
      - 水龙头拧得很小时水流速变小，为什么？ (无内容) - gyro (0 bytes) 2010-01-04, 19:26:33 (401079)
        
        我上面回答了你的问题。在最小口径处速度并不小，但出口粗就小了 (无内容) - AQuestion (0 bytes) 2010-01-04, 22:46:24 (401151)
    - 多谢。 - lightman (173 bytes) 2010-01-04, 15:53:24 (401030)
  - 这经验真够丰富的，连尿都尿过。 (无内容) - JFF (0 bytes) 2010-01-04, 14:25:47 (401017)

Thanks. 直觉觉得你是对的，不过还是有点不满意。从头问起：这里伯努利定律可以用吗？ - lightman (57 bytes) 2010-01-04, 13:57:45 (401011)

See my reply to DW below (无内容) - gyro (0 bytes) 2010-01-04, 14:01:11 (401013)