Work

功

refers to an activity involving a force and movement in the directon of the force. A force of 20 newtons pushing an object 5 meters in the direction of the force does 100 joules of work.

当力使物体沿力的方向发生位移时，这个力就对物体做了功。例如，20 牛顿的力沿自身方向推动物体移动 5 米，所做的功为 100 焦耳。

Energy

能量

is the capacity for doing work. You must have energy to accomplish work - it is like the "currency" for performing work. To do 100 joules of work, you must expend 100 joules of energy.

能量表示做功的本领。做功需要能量，可以形象地把能量看作做功所需的“货币”。要做 100 焦耳的功，就需要付出 100 焦耳的能量。

Power

功率

is the rate of doing work or the rate of using energy, which are numerically the same. If you do 100 joules of work in one second (using 100 joules of energy), the power is 100 watts.

功率表示做功或使用能量的快慢，这两种表述在数值上相同。如果在 1 秒内做功 100 焦耳，也就是在 1 秒内使用 100 焦耳的能量，功率便是 100 瓦。

Index

Work concepts

功的概念

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Work-Energy Principle

功能原理

The change in the kinetic energy of an object is equal to the net work done on the object.

物体动能的变化等于合力对物体所做的功，这就是功能原理。功能原理是解决力学问题的常用工具。它可以由能量守恒定律以及功与能量的关系导出，因此并不是一条独立于守恒定律的新规律，而是能量守恒定律在特定情形下的应用。由于许多力学问题都能借助这一原理高效求解，因此有必要把它作为一种独立的解题方法加以讨论。

This fact is referred to as the Work-Energy Principle and is often a very useful tool in mechanics problem solving. It is derivable from conservation of energy and the application of the relationships for work and energy, so it is not independent of the conservation laws. It is in fact a specific application of conservation of energy. However, there are so many mechanical problems which are solved efficiently by applying this principle that it merits separate attention as a working principle.

这一事实被称为功能原理，通常在力学问题求解中非常有用。它可以从能量守恒和功与能量关系的运用中推导出来，因此不独立于守恒定律。事实上，它是能量守恒的一个具体应用。然而，有许多力学问题通过应用这一原理得以高效解决，因此值得作为工作原理单独关注。

For a straight-line collision, the net work done is equal to the average force of impact times the distance traveled during the impact.

Average impact force x distance traveled = change in kinetic energy

平均冲击力 × 运动距离 = 动能的变化

If a moving object is stopped by a collision, extending the stopping distance will reduce the average impact force.

Car crash example 汽车碰撞示例	Seatbelt use 安全带的作用	Auto stopping distance 汽车制动距离
Large truck-small truck collision 大型卡车与小型卡车碰撞	Two trucks, equal momentum 两辆卡车，动量相等	Impact force of falling object 下落物体的冲击力
Work-energy principle for angular quantities 角量的功能原理

The rate of doing work is equal to the rate of using energy since the force transfers one unit of energy when it does one unit of work. A horsepower is equal to 550 ft lb/s, and a kilowatt is 1000 watts.

对于沿直线发生的碰撞，碰撞所做的净功等于平均冲击力乘以碰撞过程中物体移动的距离。如果运动物体因碰撞而停下，延长其停止距离就能减小平均冲击力。做功的速率等于能量转移的速率：力每做一单位的功，就转移一单位的能量。1马力等于550英尺·磅力/秒；1千瓦等于1000瓦。

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Example

索引示例

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