107 Strange Fluids-Mid

Strange Fluids FOCUS Question Why do certain fluids sometimes act like solids and other times act like liquids?

奇怪的流体焦点问题为什么某些流体有时像固体，有时像液体?

Normal Fluids Think about pouring a glass of water. The liquid quickly flows from the pitcher into the glass. Water is a fluid. A fluid can be a liquid or a gas. Water has low viscosity (vis-KOS-uh-tee). This means the fluid is not very thick. Now think about how honey moves. This fluid flows slowly. It may come out of the jar in globs. Honey has high viscosity. Different fluids have different viscosities. The temperature of a fluid can affect how it moves. If you heat up honey, it flows faster when you pour it. Its viscosity goes down. Water and honey are considered normal fluids. These fluids are affected only by temperature.

想象一下倒一杯水。 液体迅速地从水罐流进玻璃杯里。 水是流体。流体可以是液体也可以是气体。 水粘度低(vis-KOS-uh-tee)。 这意味着液体不是很稠。 现在想想蜂蜜是如何移动的。 这种液体流动缓慢。它可以从罐子里出来。 蜂蜜粘度很高。不同的液体有不同的粘度。 流体的温度会影响它的运动方式。 如果你把蜂蜜加热，当你倒蜂蜜时，它会流动得更快。 粘度下降。水和蜂蜜被认为是正常的液体。 这些流体只受温度的影响。

Strange Fluids Not all fluids act "normal," Some fluids seem like a liquid one moment and act like a solid the next. These strange fluids are affected by something other than temperature. Their viscosity changes when a force, or stress, is applied. If you hit water with your hand, not much happens. The viscosity of the water doesn't change (see black line in graph). But if you hit a strange fluid, its viscosity does change. Some strange fluids get thinner when stress is applied (see green line in graph). Others actually get thicker (see orange line in graph).

不是所有的流体都表现得“正常”，有些流体一会儿看起来像液体，一会儿又像固体。 这些奇怪的液体受温度以外的因素影响。 当施加力或应力时，它们的粘度会发生变化。 如果你用手打水，不会发生什么。 水的粘度没有变化(见图中黑线)。 但如果你碰到一种奇怪的液体，它的粘度确实会改变。 一些奇怪的流体在施加压力时变稀(见图中绿线)。 其他的反而变厚了(见图中的橙色线)。

Getting Thinner So what puts stress on a fluid? Strange fluids can respond to shaking, hitting, stirring, or squeezing. The viscosity of some strange fluids goes down when stress is applied Paint hardens if left alone in a jar. But if you shake or stir it, the paint becomes thinner. Ketchup also thins out when you add stress. Getting this fluid out of a glass bottle is difficult at first. But if you hit the bottom with enough force, the ketchup comes pouring out.

那么是什么给流体施加了压力呢? 奇怪的流体会对震动、撞击、搅拌或挤压做出反应。 一些奇怪的液体在施加压力时粘度会下降。如果把油漆单独放在罐子里，它会变硬。 但如果你摇晃或搅拌，颜料就会变薄。 当你增加压力时，番茄酱也会变稀。 一开始很难把这种液体从玻璃瓶中取出来。 但如果你用足够大的力气敲击底部，番茄酱就会喷涌而出。

Getting Thicker Oobleck is a strange fluid made of cornstarch and water. When you quickly squeeze it together in your hands, it gets thick and feels solid. But open your hands and it flows through your fingers like a liquid. Do You Know? The name "oobleck" comes from the Dr. Seuss book Bartholomew and the Oobleck. You even have a strange fluid inside your own body. This fluid is in your joints, including your knees, elbows, and shoulders When you suddenly put a lot of pressure on a joint, the fluid gets thick. This keeps your bones from rubbing together. When the stress stops, the fluid gets thin again. This allows your joints to move freely.

欧不裂是一种由玉米淀粉和水组成的奇怪液体。 当你用手快速挤在一起时，它会变厚，摸起来很结实。 但张开你的手，它就像液体一样流过你的手指。 你知道吗?“欧不裂”这个名字来自博士。 苏斯的书《巴塞洛缪与欧不裂》 你体内甚至有一种奇怪的液体。 这种液体存在于你的关节中，包括膝盖、肘部和肩膀。当你突然对某个关节施加很大的压力时，液体就会变厚。 这样可以防止骨头互相摩擦。 当压力停止时，液体又变稀了。 这可以让你的关节自由活动。

Stress over Time Some strange fluids change instantly when a force is applied. Others change only when the stress lasts for a longer time. Have you ever made whipped cream? When you start, the cream is a liquid that can easily pour. But after whipping it for a few minutes, the cream becomes thick. If you let it sit for a while, it acts like a liquid again. Other fluids have the opposite response to stress over time. Think about squeezing hair conditioner from a bottle. The liquid is very thick. When you shake it for a while, the conditioner becomes thinner and pours from the bottle. If you stop shaking it, it becomes a thicker fluid again.

随时间变化的压力有些奇怪的流体在施力时立即发生变化。 另一些只有在压力持续较长时间时才会改变。 你做过鲜奶油吗? 当你开始时，奶油是一种很容易倒出的液体。 但搅拌几分钟后，奶油就变稠了。 如果你让它静置一段时间，它又会像液体一样。 随着时间的推移，其他液体对压力有相反的反应。 想象一下从瓶子里挤出护发素。 这液体很浓。摇一摇，护发素就会变稀，从瓶子里倒出来。 如果你停止摇晃它，它又会变成更稠的液体。