91 Science Friction-Mid

Science Friction FOCUS Question How is friction related to heat energy?

摩擦与热能有什么关系?

Warm Up with Friction It's a cold day, and you forgot your mittens. You rub your chilly hands together. Suddenly they feel warmer. Where did that warmth come from? The warmth in your hands came from heat energy generated by friction. Friction is a force. It acts between objects that rub against each other. Friction also causes moving things to slow down. It changes the energy of a moving object from motion into heat.

用摩擦热身天气很冷，你忘了带手套。 你搓着冰冷的双手。 突然他们觉得暖和了。 这种温暖从何而来? 手上的热量来自于摩擦产生的热能。 摩擦力是一种力。它作用于相互摩擦的物体之间。 摩擦也会使运动的物体减速。 它把运动物体的能量从运动转化为热量。

What Is Friction? You use friction every day. When you walk, run, jump, and stop, your feet touch the ground and create friction. If you wear skates with wheels, you have less friction with the ground. Zoom! Friction happens between all kinds of matter— solids, liquids, and gases. Matter makes up everything around you. All matter is made of tiny particles. When things rub together, the edges of the particles catch. This is friction. Friction happens whenever matter touches. As particles catch and pull apart again, they move back and forth. The movement of particles is heat.

什么是摩擦?你每天都在使用摩擦。 当你走、跑、跳和停下来时，你的脚接触地面并产生摩擦。 如果你穿有轮子的冰鞋，你与地面的摩擦就会减少。 祖姆！摩擦发生在各种物质之间——固体、液体和气体。 物质构成了你周围的一切。 所有物质都是由微小的粒子构成的。 当物体相互摩擦时，粒子的边缘会相互吸引。 这是摩擦力。只要物质接触，就会发生摩擦。 当粒子再次相遇和分离时，它们就会来回移动。 粒子的运动就是热。

Factors of Friction It's harder to walk through water than through air. If you run through water. it only gets harder. Water has more particles in the same amount of space than air does. More particles mean more friction. As speed increases, so does friction. Mass, or the amount of matter, creates more friction. It is easier to push an empty box than a full one. The size of a surface can also affect friction. It is easier to push a skinny box than a wide box. A rough surface causes more friction. It's easier to push a box across a smooth floor than across a carpet.

摩擦的因素在水中行走比在空气中更难。 如果你在水中奔跑。这只会越来越难。 在同样的空间里，水比空气含有更多的粒子。 更多的粒子意味着更多的摩擦。 随着速度的增加，摩擦力也随之增加。 质量，或物质的数量，会产生更多的摩擦。 推一个空盒子比推一个满盒子容易。 表面的大小也会影响摩擦。 推一个细箱子比推一个宽箱子容易。 粗糙的表面引起更多的摩擦。 在光滑的地板上推箱子比在地毯上推容易。

Fire from Friction Friction changes motion into heat. Lots of friction makes lots of heat If wheels are moving fast enough, the tires will start to smoke and burn (see cover). At times you can get enough heat to start a fire! Matches use friction to create a flame. The head of a match catches fire at a fairly low temperature. The match lights when it is rubbed quickly across a rough surface. This friction gives off heat, so the match catches fire. Some people can light a fire by rubbing two sticks together. Wood must be at a much higher temperature than a match head before it will catch fire. It takes a lot of skill—and a lot of patience—to light a fire by using friction Safety! Never light matches without the help of an adult.

摩擦把运动变成热。 如果车轮移动得足够快，轮胎就会开始冒烟并燃烧(见封面)。 有时你可以得到足够的热量来生火!火柴通过摩擦产生火焰。 火柴头在相当低的温度下就会着火。 火柴在粗糙的表面上快速摩擦时就会发光。 这种摩擦散发出热量，所以火柴就着火了。 有些人可以通过摩擦两根木棍来生火。 木头的温度必须比火柴头的温度高得多，才会着火。 用摩擦生火需要很多技巧和耐心。没有大人的帮助，千万不要点燃火柴。

Machinery and Friction Machines can create lots of friction and, as a result, lots of heat. When machines get too hot, their parts can short-circuit, melt, or even catch fire. Many machines have ways to prevent friction. Some have tiny parts called ball bearings between their moving parts. The bearings roll past each other. Rolling causes a lot less friction than sliding. Other machines use lubricants, or slippery materials, to prevent friction. Oil and grease are lubricants. Some machines need friction to do their jobs. A saw can't cut wood without rubbing against it, but the motion heats the blade. When machines get too hot, people cool them using water, fans, or air conditioners.

机械和摩擦机械会产生大量摩擦，从而产生大量热量。 当机器温度过高时，零件可能会短路、熔化，甚至着火。 许多机器都有防止摩擦的方法。 有些在它们的活动部件之间有一个叫做球轴承的小部件。 轴承相互滚动。 滚动产生的摩擦比滑动小得多。 其他机器使用润滑剂或光滑的材料来防止摩擦。 油和润滑脂都是润滑剂。 有些机器需要摩擦才能工作。 锯切木头时必须与木头摩擦，但这种摩擦会使锯片发热。 当机器太热时，人们用水、风扇或空调来冷却它们。