U3W1 FORCES AT WORK

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FORCES AT WORK

工作中的力量

CHAPTER 1 FORCES A force pushes or pulls something. A force happens when two objects interact, or when one object does something to the other. Forces affect how objects move on Earth and in space. Forces are at work around you all the time. A push is a force that makes the swing move.

第1章 力 力能够推或拉某个物体。当两个物体相互作用，或者一个物体对另一个物体施加作用时，就会产生力。 力影响着地球上以及太空中的物体运动。力无时无刻不在你周围起作用。 推是一种能使秋千摆动的力。

You use forces to make things move every day. When you push on a door, it swings open. At the grocery store, a cart moves if you push it. A door closes behind you when you pull it shut. When you pull on a drawer handle, the drawer opens. Pulling is a force that makes the wagon move.

你每天都在运用力使物体移动。当你推门时，门就会摆动打开。在杂货店，如果你推购物车，它就会移动。当你拉门时，门会在你身后关上。当你拉动抽屉把手时，抽屉就会打开。 拉是一种使手推车移动的力。

Gravity is a force that pulls objects. You can't see gravity, but you know it is at work. On Earth, gravity pulls objects toward the ground. Gravity pulls you down too. It keeps you from flying into space! You can show the effects of gravity easily. Drop a pencil. What happened? The pencil fell to the ground. Why? Gravity pulled it down. You just proved that gravity works! Because of gravity, the tomatoes push down on the scale.

重力是一种吸引物体的力。你看不见重力，但你知道它在起作用。在地球上，重力把物体拉向地面。重力也把你往下拉。它使你不会飞到太空去! 你可以很容易地证明重力的作用。扔一支铅笔。发生了什么?铅笔掉到了地上。为什么呢?是重力把它拉下去了。你刚刚证明了重力的存在! 由于重力的作用，西红柿会对秤产生向下的压力。

Friction is another force that affects how things move. It is different from gravity. Gravity works without objects touching each other. But friction is a contact force. It works when two objects rub against each other. lt slows down moving objects. Feel Friction at Work You can feel friction. Rub your hands together quickly. Feel the heat? It is caused by friction. Friction between the mug and the table slows the mug down when you push it.

摩擦力是另一种影响物体运动方式的力。它与重力不同。重力在物体不相互接触时也会起作用。但摩擦力是一种接触力。当两个物体相互摩擦时，摩擦力就会起作用。它会减慢运动物体的速度。 感受摩擦力的作用 你能感受到摩擦力。快速搓搓你的手。感觉到热了吗?这是由摩擦力引起的。 当你推动杯子时，杯子和桌面之间的摩擦力会使杯子减速。