Chapter 3 Force and Newton s laws
Chapter 3 Force and Newton’s laws
Section 3-1 Classical mechanics The approach to the dynamics we consider here is generally called classical mechanics Galileo Galilei Issac Newton (1564-1642)(1642-1727
Issac Newton (1642－1727） Galileo Galilei (1564－1642） Section 3-1 Classical mechanics • The approach to the dynamics we consider here is generally called classical mechanics
In this chapter, we will study in detail the bases of classical mechanics: Newtons three laws Classical mechanics was found not to describe well the motions in certain realms For ordinary objects, classical mechanics is important and very useful
• In this chapter, we will study in detail the bases of classical mechanics: Newton’s three laws. • Classical mechanics was found not to describe well the motions in certain realms. • For ordinary objects, classical mechanics is important and very useful
Section 3-2 Newtons first law What can cause the motion of a body? Force Take the apple's freely falling motion as an example What will be the states of the body if there is no any interactions between it and its environment? (an isolated system) At rest or 1D uniform motion Newton's first law Every body continues in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it
Section 3-2 Newton’s first law ▪ Newton’s first law : Every body continues in its state of rest or uniform motion in a straight line, unless it is compelled to change that state by forces impressed on it. ▪ What can cause the motion of a body? Take the apple’s freely falling motion as an example Force ▪ What will be the states of the body if there is no any interactions between it and its environment? (an isolated system) At rest or 1D uniform motion
1. Newton's first law tells us Consider a body on which no net force acts 1)If the body is at rest, it will remain at rest; 2)If the body is moving with constant velocity, it will continue to do so, no force is needed to keep it moving
1. Newton’s first law tells us: Consider a body on which no net force acts. 1) If the body is at rest, it will remain at rest； 2) If the body is moving with constant velocity, it will continue to do so, no force is needed to keep it moving