Newton's Laws - Lesson 1 - Newton's First Law of Motion

State of Motion

Inertia is the tendency of an object to resist changes in its state of motion. But what is meant by the phrase state of motion? The state of motion of an object is defined by its velocity - the speed with a direction. Thus, inertia could be redefined as follows:

Inertia: tendency of an object to resist changes in its velocity.

Newton's First Law

Newton's First Law States: an object at rest stays at rest, an object in motion stays in motion with a

Newton's Second Law

If 0 (i.e. there is a net external force acting on an object) then,
 

= m.

(2)

Definition: Inertia is the tendancy of an object to resist any attempt to change its state of motion.

Newton's Third Law

Idea: Forces in nature always exist in pairs. Newton's third law states: For every action, there is an equal and opposite reaction. When two bodies interact:

= - .

(4)

Where is the force exerted on body 1 by body 2 and is the force exerted on body 2

Applications of Newton's Laws

Assumptions:

• We treat objects as point