Free Body Diagram & Basic Mechanics（自由體圖概念與力學基礎）

　　本書是基礎力學的簡介，其中重點介紹自由體圖的概念。此概念是學習力學的第一個最重要的抽像概念。本書的特點是引導讀者經過簡單的例題計算來呈現此概念，而不是直接描述。有了這概念的基礎理解後，我們將細緻化自由體圖的概念，更整理為一套可操作的法則，以按此法則用作更複雜的力學解題。本書可作為雙語學習的參考教材。

About the Author

Dr. K. L. Lee

　　The author was graduated from The Chinese University of Hong Kong, with the degree of PhD in Physics. He has many years of experience in both engineering and teaching work. He has been working in the field of materials science. He is also experienced in teaching in universities and international school. In particular, he wanted to record his experience in his teaching about the concepts in basic mechanics.

作者簡介

李家麟

　　作者畢業於香港中文大學、物理學博士學位。作者是材料科學方面的科技工作者，有多年工程及教育工作經驗，曾任教於大學和國際學校。作者希望把教學經驗記錄下來。本書為其在力學方面的教學心得。
 

Section A: What is Force
 
Law of Force, Origin of Force
 
What is Force
 
The Intuitive Meaning of Force
 
You feel a force when someone pushes you.
 
A force is a push or pull upon an object by another object when the two objects interact with each other.
 
The Effect of a Force
 
A force is a push or pull. So we consider the effect of such push and pull to narrow down the actual meaning of ‘Force’.
 
Let us consider the motion of an object exerted by a force, for example, dragging a luggage. Let us use our intuition to judge: which of the following intuition is correct.
 
Intuition 1:
 
A pulling force is needed to keep the motion of the luggage.
 
That is, a force is needed to keep an object in motion.
 
Intuition 2:
 
A pulling force is needed to start the motion of the luggage.
 
That is, a force is needed to speed up the motion of an object.