摩擦

Lesson Objectives
::经验教训目标

• Describe friction and how it opposes motion.
  ::描述摩擦和它如何反对运动。

• Identify types of friction.
  ::确定摩擦的类型。

Lesson Vocabulary
::词汇表课程

• fluid
  ::液液

• friction
  ::摩擦

Introduction
::导言

Did you ever rub your hands together like the child in the  Figure  ? Why did you do that? A common answer would be to warm your hands. Why does this make your hands warmer? The answer is friction. So what exactly is friction? 
::你们曾经像图中的孩子一样双手相握吗?为什么你们这样做?一个共同的答案是暖和你的手。为什么这能让你的手更暖和?答案是摩擦。究竟什么是摩擦?

 

What Is Friction?
::什么是摩擦?

Friction  is a force that works against motion. It occurs between two surfaces that are touching. Friction can be good and bad. How can this be? Think about some common things we do. For example, we put rubber tires on our cars. The tires cause friction against the road. Without rubber tires, the car would slide around. Think about the bottom of your bathtub. Do you have tape that has a sandy texture? Maybe you use a rubber mat. Both materials prevent you from slipping. If you live in a really cold place, you have probably seen icy sidewalks. Perhaps you have put sand on the frozen surface. The sand increases friction. It helps to keep you from slipping and falling. Is friction always a good thing? 
::摩擦是反对运动的力量。 它发生在两个感动的表面之间。 摩擦可以是好的,也可以是坏的。 这怎么可能呢? 想想一些共同的东西。 比如, 我们把橡胶轮胎放在我们的汽车上, 轮胎会对路造成摩擦。 没有橡胶轮胎, 汽车会滑动。 想想浴缸底部。 你有带沙质的胶带吗? 或许你用一个橡胶垫。 两种材料都防止你滑倒。 如果你生活在一个非常冷的地方, 你也许已经看到了冰滑的人行道。 也许你把沙子放在了冰冻的表面。 沙子会增加摩擦。 它会帮助你避免滑落和跌倒。 摩擦总是好事吗?

Too much friction can also be harmful. What about the oil in a car? What does it do? The engine oil helps to reduce friction in car engines. Too much friction can wear out the parts. Can you think of other times when friction is not beneficial?
::太多的摩擦也可能有害。 汽车中的石油会怎样? 它会怎样? 发动机油有助于减少汽车引擎中的摩擦。 太多的摩擦会耗尽零件。 你能想象到其他摩擦无益的时候吗?

Other examples of friction are illustrated in the  Figure  . 
::图3显示了其他摩擦的例子。

 

Why Friction Occurs
::为何会发生摩擦

Feel the top of your desk. Does it look and feel smooth? Yes, it feels and looks smooth, but is it really? Even when surfaces look smooth to the unaided eye, they may not be. Scientists use a microscope to look at things more closely. Through a microscope, smooth surfaces may appear rough or bumpy. Look at the metal surfaces in the  Figure  . The metal foil is so smooth that it is shiny. However, when highly magnified, it is clearly not smooth. It actually looks to be very bumpy. All those bumps grab the bumps of other surfaces. They grind together. They oppose the motion of the two surfaces. Now you know what causes friction.
::感觉你桌子的顶部。 它看起来和感觉很平滑吗? 是的, 它感觉和看起来很平滑, 但真的吗? 即使表面看起来光滑, 它们可能不是。 科学家们用显微镜更仔细地观察事物。 通过显微镜, 光滑的表面可能看起来粗糙或模糊。 看看图中的金属表面。 金属粉尘是如此光滑, 它闪亮。 但是, 当高度放大时, 它显然不光滑。 它看起来确实很不平滑。 所有这些撞击都抓住了其他表面的撞击。 它们一起磨碎了。 它们反对两个表面的运动。 现在你知道是什么导致摩擦了 。

 

Factors That Affect Friction
::影响拼音的因素

Rough surfaces create more friction than smooth surfaces. That’s why cars have tires. It's also why we use rubber mats in areas that might get wet. In your bathtub, you may even use "No-Slip" tape. "No-slip" is another way of saying the items have a lot of friction.
::粗糙的表面比平滑的表面产生更多的摩擦。这就是为什么汽车有轮胎的原因。这也是为什么我们在可能湿润的地区使用橡胶垫的原因。在你的浴缸里,你甚至可以使用“不滑动”胶带。“不滑动”是另一种说这些物品有很多摩擦的方式。

In the  F igure  , the blades of the skates are very smooth. That’s why you can’t slide across ice with shoes. The soles of your shoes are much rougher than skates. The rougher surface of shoes causes more friction and slows you down.
::在图中,滑冰的刀片非常平滑。 这就是为什么你不能用鞋滑过冰块。 你的鞋底比滑冰鞋要粗糙得多。 鞋的粗糙表面造成更多的摩擦,拖慢了你们的脚步。

Heavier objects also have more friction. A heavy object presses down with more force. The surfaces are held together more tightly. This makes the surfaces harder to slide past each other. Did you ever try to push something heavy across the floor? Heavy objects are much harder to push than light objects. 
::较重的物体也有更多的摩擦。 重物体会用更大的力力按下。 表面会更紧紧地固定在一起。 这使得表面更难滑过对方。 您有没有试图将重物推过地面? 重物体比光物体更难推。

 

Friction Produces Heat
::热能

You know that friction also causes heat. Think about when you rub your hands together. It is friction that makes them warm. But why does this happen?
::你知道摩擦也会引起热。 想想当你们一起抚摸双手的时候, 是摩擦让他们暖和起来的。 但为什么会这样呢?

Friction causes the molecules on rubbing surfaces to move faster. Faster moving particles have more heat energy. Heat from friction can be useful. Can you think of other places where you might find friction? 
::摩擦使摩擦表面上的分子移动速度更快。 快速移动的粒子具有更多的热能。 摩擦产生的热能可能有用。 您能想到其它您可能发现摩擦的地方吗 ?

Friction also lets you light a match (see  Figure  ). Heat from friction can also cause problems. It can cause a car to overheat. To reduce friction, oil is added to the engine. Oil coats the surfaces of moving parts. This coating of oil makes them slippery. When things are slippery there is less friction. 
::摩擦产生的热也会造成问题。 它可能会导致汽车过热。 为了减少摩擦, 引擎会添加油。 油会覆盖移动部件的表面。 这种油层涂层会滑。 当事情滑动时, 摩擦会减少 。

Have you ever seen a sign that says, "slippery when wet?" This too has to do with friction. Water, like oil, can reduce friction. The wet surface may allow your shoes to slide more easily. This situation may cause the potential to fall. Think about the rubber mats just inside many doorways. Why do you think they are there? 
::你有没有见过一个迹象,上面写着“湿润时滑动?” 这和摩擦有关?水像石油一样,可以减少摩擦。湿的表面可以更容易地使你的鞋滑动。这种情况可能会导致可能下降。想想许多门道内的橡胶垫子。你为什么认为它们在那里?

 

Lesson Summary
::经验教训摘要

• Friction is a force that opposes motion. It occurs between two surfaces that are touching. Friction occurs because no surface is perfectly smooth. Friction is greater when objects have rougher surfaces. It is also greater when objects are heavier. The increased weight causes surfaces to press together with greater force.
  ::摩擦是一种反对运动的力量。 它发生在两个触碰的表面之间。 摩擦发生是因为没有表面完全平滑。 当物体表面较粗糙时, 摩擦会更大。 当物体变重时, 摩擦也会更大。 增加的重量会使表面与更大的力一起压在一起。

Lesson Review Questions
::经验回顾问题

Recall
::回顾

1. What is friction?
   ::什么是摩擦?

1. List factors that affect friction.
   ::列出影响摩擦的因素。

1. How does friction produce heat?
   ::摩擦如何产生热?

Apply Concepts
::应用概念

4. Explain why are rubber mats are placed near doorways on rainy days.
   ::解释为什么在雨天时橡胶垫被放在门口附近。

Think Critically
::仔细仔细思考

5. Explain why friction occurs.
   ::解释为什么会发生摩擦