A gas is comparatively easy to compress. Changes of volume with pressure are large, cannot normally be neglected and are related to changes of temperature. A given mass of gas has no fixed volume and will expand continuously unless restrained by a containing vessel. It will completely fill any vessel in which it is placed and, therefore, does not form a free surface.
1 Newtonian and non-Newtonian Fluids
Newtonian fluids:
Fluids which obey the Newton's law of viscosity are called as Newtonian fluids. Newton's law of viscosity is given by
t = mdv/dy
where t = shear stress
m = viscosity of fluid
dv/dy = shear rate, rate of strain or velocity gradient
All gases and most liquids which have simpler molecular formula and low molecular weight such as water, benzene, ethyl alcohol, CCl4, hexane and most solutions of simple molecules are Newtonian fluids.
3 Physical properties:
Viscosity
The viscosity (m) of a fluid measures its resistance to flow under an applied shear stress. Representative units for viscosity are kg/(m.sec), g/(cm.sec) (also known as poise designated by P). The centipoise (cP), one hundredth of a poise, is also a convenient unit, since the viscosity of water at room temperature is approximately 1 centipoise.
The kinematic viscosity (n) is the ratio of the viscosity to the density:
n = m/r,
and will be found to be important in cases in which significant viscous and gravitational forces exist.
Viscosity of liquids:
Viscosity of liquids in general, decreases with increasing temperature.
The viscosities (m) of liquids generally vary approximately with absolute temperature T according to:
ln m = a - b ln T
Viscosity of gases:
Viscosity of gases increases with increase in temperature.
The viscosity (m) of many gases is approximated by the formula:
m = mo(T/To)n
in which T is the absolute temperature, mo is the viscosity at an absolute reference temperature To, and n is an empirical exponent that best fits the experimental data.
The viscosity of an ideal gas is independent of pressure, but the viscosities of real gases and liquids usually increase with pressure.
Viscosity of liquids are generally two orders of magnitude greater than gases at atmospheric pressure. Fow example, at 25oC, mwater = 1 centipoise and mair = 1 x 10-2centipoise.
Vapor Pressure
參考答案:气体是比较容易压缩。 容量的变动以压力是大，不可能通常被忽略和与温度变化有关。 气体特定大量没有固定的容量，并且连续扩展，除非由一艘包含的船克制。 它完全地将填装安置它，并且，因此，不形成自由表面的所有船。
1牛顿和non-Newtonian流体
牛顿流体：
服从黏度牛顿的法律的流体叫作为牛顿流体。 给黏度牛顿的法律
t = mdv/dy
那里t =抗剪应力
流体m =黏度
dv/dy =剪张力的率、率或速度梯度
有更加简单的分子式和低分子量例如水、苯、乙醇、CCl4、己烷和简单的分子的多数解答的所有气体和多数液体是牛顿流体。
3有形资产：
黏度
流体的黏度(m)测量它的对流程的抵抗在应用的抗剪应力之下。 代表性单位为黏度是公斤(m。秒)， g/(cm。秒) (亦称P选定的世故)。 centipoise (控制点)，百分之一世故，也是一个方便单位，因为水黏度在室温是大约1 centipoise。
运动学黏度(n)是黏度的比与密度：
n = m/r，
并且将被发现重要的在重大黏和引力存在的案件。
液体黏度：
随着温度的增加，液体黏度一般来说，减少。
黏度液体(m)随绝对温度T近似地一般变化根据：
ln m = a至b ln T
气体黏度：
气体黏度增加以在温度的增量。
黏度许多气体(m)由惯例接近：
m = mo (T/To) n
在哪T是绝对温度， mo是黏度在一个绝对参考温度对，并且n是经验主义的方次数那最佳的适合实验性数据。
一完全气体的黏度是压力的独立，但真正的气体和液体黏度通常增加以压力。
液体黏度一般是二个数量级大于气体以大气压。 Fow例子，在25oC、mwater = 1 centipoise和mair = 1 x 10-2centipoise。
汽压
