✔ 最佳答案
1. In practice, you could regard liquids as imcompressible because most liquids have a large bulk modulus (e.g. water: 2.15 x 10^9 Pa), whereas gases have much lower bulk modulus (e.g. air: 1.42 x 10^5 Pa). Liquids are thus much much harder to compress.
2. In fact, pressure at a point exerts in all direction. This is one of the inherent properties of fluid pressure.
The "arrows" only indicates the directions of pressure that are of relevance to the explanation of Bernoulli's Prinicple.
3. Your question is not clear. Is there any specific example?
2011-08-31 20:02:10 補充：
Q:咁點解bunsen burner入面又可以用continuity 條式??..佢入面係gas
A: why not ? Continuity equation is just another interpretation of "conservation of mass". The flow of gas in a bunsen burner observes mass conservation.
2011-08-31 20:03:49 補充：
Q:咁佢地既pressure value 一5一樣???
A: any fluid (liquid or gas) flows from high to low pressure. The same principle applies to the flow of gas in a bunsen burner.
