Define force, and give examples of forces. ::定义武力,并举例说明武力。
Describe how forces combine and affect motion. ::描述各种力量如何结合并影响运动。
Lesson Vocabulary ::词汇表课程
force ::强力力力
net force ::净额 净额 部队净额 净额
newton (N) ::牛顿( N)
Introduction ::导言
What causes a change in motion? The application of a force. Any time an object changes motion, a force has been applied. In what ways can this happen? ::是什么导致运动的改变? 武力的应用。 任何时间, 物体改变运动, 武力已经应用。 以什么方式发生这种情况?
Force can cause an object at rest to start moving. Forces can cause objects to speed up or slow down. Forces can cause a moving object to stop. Forces can also cause a change in direction. In short, forces cause changes in motion. The moving object may change its speed, its direction, or both. ::强制可以在休息时导致对象开始移动。 力量可以使对象加速或放慢速度。 力量可以使移动对象停止。 力量也可以使方向发生变化。 简言之, 力量可以使运动发生变化。 移动对象可以改变其速度、 方向或两者都改变 。
We know that changes in motion require a force. We know that the size of the force determines the change in motion. How much an object's motion changes when a force is applied depends on two things. It depends on the strength of the force. It also depends on the object's mass. ::我们知道运动的改变需要力量,我们知道力量的大小决定运动的改变。当使用武力时,物体的动作变化多少取决于两点。它取决于力量的强度。它也取决于物体的质量。
Think about some simple tasks you may regularly do. You may pick up a baseball. This requires only a very small force. Next, you toss the baseball to a friend. This takes a little larger force. With an even bigger force, you can throw it to your other friend far across the field. The larger the force applied, the bigger the change in motion. ::想想一些你可能经常做的简单任务。 你可以拿起棒球。 这只需要一小股力量。 下一步, 你把棒球扔给朋友。 这需要更大的力量。 更大的力量, 你可以把它扔给你的另外一位朋友。 势力应用得越大, 运动的变化就越大 。
Think about these actions if the ball was a bowling ball. What kind of force would it take to pick it up? Would it be more than the force needed to pick up a baseball? What about if you were to toss the bowling ball? Is it even possible to throw the bowling ball any distance? This demonstrates how the size of the force depends on the object's mass. As you increase the mass of the object, the harder it is to cause a change in its motion. ::想想这些动作, 如果球是一个保龄球的话。 需要什么样的力量才能把它捡起来? 是否比捡起棒球需要的力量更多? 如果你扔了保龄球呢? 能不能抛出保龄球任何距离? 这可以说明保龄球的大小取决于物体的质量。 当你增加物体的重量时, 改变物体运动的难度就更大了 。
Defining Force ::定义力力
Force is defined as a push or a pull. Another example of force is an applied force. It occurs when a person or thing applies force to an object. You can see an example of this in Figure . The force of the push causes the swing to move. ::力被定义为推力或拉力。另一个力的例子就是施用力。当一个人或某物对物体施压时,力就会发生。图中可以看到这个例子。推力促使摆动。
Sometimes forces are less obvious. How about friction, magnetism, and gravity? They all can cause a force. ::有时力量不那么明显。摩擦、磁力和引力呢?它们都可以产生力量。
When this girl pushes the swing away from her, it causes the swing to move in that direction.
Force as a Vector (Advanced Topic) ::作为矢量强制力( 高级主题)
Force is a vector. What then is a vector? Think about how you would give directions to a friend. You would not say, just walk half a mile. The person may walk a half mile in the wrong direction! More information is needed. You may say, follow this particular road for a half mile. You may say, look for the green house on Sumter St. In both examples, you provided a direction. You also gave the distance. In other words, you provided a vector. You did not just give a distance. Both pieces of information are needed to find a location. This is just like describing forces. To explain forces, both size and direction are needed. ::强制是向量。 那么是向量 。 想想你会如何向朋友提供方向 。 您不会说, 只需走半英里 。 这个人可能走半英里错误的方向 。 需要更多的信息 。 您可以说, 沿着这条特定的道路走半英里 。 您可以说, 在两个例子中, 寻找Sumber St. 的绿屋, 您也提供了方向 。 您也给出了距离 。 换句话说, 您提供了一个向量 。 您没有给出距离 。 您没有给出一个距离 。 需要两条信息来找到一个位置 。 这就像描述力量一样 。 解释力量, 大小和方向都是需要的 。
Notice the girl in Figure . She is pushing the swing away from herself. That's the direction of the force. She can give the swing a strong push or a weak push. That's the size, or strength, of the force. ::注意图中的女孩。她正在将秋千推离自己。这是力量的方向。她可以给秋千一个强大的推力或微弱的推力。这就是力量的大小或强度。
Arrows are used to show a force. Figure shows some examples. The length of each arrow tells you about the strength of the force. The way the arrow points tells you about the direction of the force. Both are necessary to explain a force. How could you use an arrow to explain the girl's push on the swing? ::箭头用于显示力量。 图显示一些例子。 每支箭头的长度可以告诉您力量的强度。 箭头指针向您说明力量方向的方式。 两者对于解释力量都是必要的。 您如何用箭头来解释女孩在秋千上的推力?
Forces can vary in both strength and direction.
SI Unit of Force ::SI 部队单位
A scientist would measure a force in a unit called a newton (N). The newton was named for scientist Sir Isaac Newton. He is famous for his law of gravity. ::科学家将测量一个单位的威力,单位名称是牛顿(N)。牛顿被命名为科学家伊萨克·牛顿(Isaac Newton)爵士。他以重力定律而出名。
Combining Forces ::联合部队
What if two children push a swing at the same time? Would the swing go higher? Yes, together their force would be more. It is common for forces to be combined. Most objects on Earth have at least two forces acting on them. Do you know what one of them is? Of course, that force is gravity. ::如果两个孩子同时推下秋千呢? 秋千会高一点吗? 是的, 他们的力量会更大。 合并力量是常见的。 地球上的大多数物体至少有两股力量在他们身上行动。 你知道他们其中的一支是什么吗? 当然, 这支力量就是引力。
How many forces do you have on you right now? Gravity pulls you down toward the center of Earth. Your legs exert a downward force. They hold you up against the pull of gravity. ::重力将你拉向地球中心,你的双腿向下拉力。它们将你挡在引力的拉动下。
Consider the example in Figure . A book is resting on a table. Gravity pulls the book downward. It has a force of 20 newtons. At the same time, the table pushes the book upward. Its force is also 20 newtons. The table opposes the pull of gravity. If not, it would fall to the ground. The two forces combine to hold the book in place. In this case, they keep it from moving. ::以图中为例。 一本书正停留在一张桌子上。 重力将书拉下。 它有20个牛顿的力量。 同时, 表格将书推向上。 其力也是20个牛顿。 表格反对引力的拉动。 否则, 它会掉到地上。 两支力量合在一起将书固定在原地。 在这种情况下, 它们不让它移动 。
Combined forces are called net forces. In the case of the book, the forces are balanced. This takes into account all of the individual forces acting on the object. ::就本书而言,部队是平衡的,这考虑到在目标上行动的所有个别部队。
A book resting on a table is acted on by two opposing forces.
Forces Acting in Opposite Directions ::对面指挥部队
What happens when two forces act in opposite directions? Net force is the difference between the two forces. In other words, one force is subtracted from the other. Think back to the book example. One force was opposite the other. The forces were equal in each direction. In this case, the net force is zero. Because the forces on the book are balanced, the book doesn't move. It does not fall to the ground. The table is not breaking. The book is not falling to the ground. Both are evidence that the force are balanced. ::当两支部队以相反方向行动时会怎样呢? 净力是两支部队之间的差别。 换句话说, 一支部队从另一支部队中减去。 回想一下书本的例子。 一支部队在另一支部队之间对着另一支部队。 每支部队在每一个方向上是相等的。 在这种情况下, 净力是零。 因为书上的力量是平衡的, 书不会移动。 书不会掉到地上。 表格没有破损。 书没有掉到地上。 两者都证明了部队是平衡的。
Situations like these are common. Can you think of objects sitting on shelves or tables? These are all examples of balanced forces. Thanks to balanced forces objects stay where you put them. ::像这样的情况是常见的。 你能想到坐在架子或桌子上的东西吗? 这些都是平衡力量的例子。 多亏了平衡力量, 物体才会留在你放置的地方 。
Woof! Woof! Look at the dogs playing tug-of-war. Both dogs are pulling on the rope. Each pulls in an opposite direction. One is pulling on the rope to the left. He pulls with a force of 10 newtons. The other dog is pulling on the rope to the right. He pulls with a force of 12 newtons. These forces are not equal. Therefore, they are not balanced. ::呜!呜!看那些狗在拖战,两只狗在拉绳,两只狗在拉绳,两只向相反方向拉绳,一只向左拉绳,一头用10牛顿的力量拉绳,另一只狗在拉绳,一头用12牛顿的力量拉绳,两只不相等。所以,两只力量不是平衡的。
What does it mean when the forces are not balanced? The net force is greater than zero. The net force on the rope is 2 newtons to the right. This is the difference between the two forces. In this instance, the rope will move to the right. Not surprising, the bigger dog is providing the largest force. ::当力量不平衡时,这意味着什么?净力量大于零。绳子上的净力量是右边的2个牛顿。这是两股力量的区别。在这种情况下,绳子会向右移动。不足为奇的是,更大的狗狗提供了最大的力量。
When unbalanced forces are applied to an object in opposite directions, the smaller force is subtracted from the larger force to yield the net force.
Forces Acting in the Same Direction ::在同一方向行动的部队
What if two forces act in the same direction? You can see an example of this in Figure . One man lifts a piece of furniture. He moves to the right with a force of 25 newtons. His co-worker helps him lift the piece of furniture. He also moves to the right with a force of 20 newtons. The forces are in the same direction. Therefore, the forces are added together. The net force equals the sum of the two forces. It is more than either of the forces by themselves. ::如果两支部队在同一方向采取行动呢?你可以看到图中的一个例子。一个人举起一具家具,他以25个牛顿的力量向右移动,他的同事帮助他抬起家具,他也以20个牛顿的力量向右移动,部队也朝同一方向移动。因此,部队是聚集在一起的。净部队等于两支部队的总和。部队本身比两个部队都多。
When two forces are applied to an object in the same direction, the two forces are added to yield the net force.
You Try It! ::你试试看!
The boys in the drawing above are about to kick the soccer ball. They are kicking the ball from opposite directions. What will be the net force on the ball? In which direction will the ball move?
Lesson Summary ::经验教训摘要
Force is a push or a pull acting on an object. Examples of force include friction and gravity. Force is a vector because it has both size and direction. The SI unit of force is the newton (N). ::强制是指对对象的推力或拉动动作。 武力的例子包括摩擦和重力。 武力是矢量, 因为它既有大小,也有方向。 SI的武力单位是牛顿( N ) 。
The combined forces acting on an object are called the net force. When forces act in opposite directions, they are subtracted to give the net force. When they act in the same direction, they are added. This gives us the net force. ::在一个物体上行动的联合部队称为净部队,当部队向相反方向行动时,它们被减为提供净部队,当它们朝同一方向行动时,它们被加为净部队,这给我们提供了净部队。
Lesson Review Questions ::经验回顾问题
Recall ::回顾
Define force. Give an example of a force. ::定义力。请举一个例子力。
What is a newton? ::什么是牛顿?
What is net force? ::什么是净力量?
Describe an example of balanced forces and an example of unbalanced forces. ::描述一个平衡力量的例子和一个不平衡力量的例子。
Apply Concepts ::应用概念
What is the net force acting on the block in each diagram below?
::下图中每个区块的 净力是多少?
Think Critically ::仔细仔细思考
Explain how forces are related to motion. ::解释一下力量与运动的关系
Points to Consider ::需要考虑的要点
In the next lesson, "Friction," you will read about the force of friction. You experience this force every time you walk. It prevents your feet from slipping out from under you. ::在下一个课中,“战斗”,你会读到摩擦的威力。每次走路时,你都要体验这种威力,以免脚从你的下面滑出来。
How would you define friction? ::你怎么定义摩擦?
What do you think causes this force? ::你认为是什么导致了这股力量?
