Newton’s third law of motion (textbook p:102-103)

Newton’s third law

• Newton’s third law states that when 2 objects A and B are in interaction, they exert forces on each others

Newton’s third law

• Examples:1. When you push a box, the box pushes you back

Newton’s third law

• Examples:2. Flying gracefully through the air, birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.

Newton’s third law

• Examples:3. The baseball forces the bat to the left (an action); the bat forces the ball to the right (the reaction).

Newton’s third law

• Examples:4.

Newton’s third law

• Examples:4. The earth exerts on the chair the force of gravity (action force), the chair exerts a force on the earth (reaction force)

Newton’s third law

- Note that action and reaction forces are of the same type ( both contact or both field forces)

- They are equal in magnitude, opposite in directions.

- They are simultaneous exerted by an object on the other ( the system and agent are reversed)

- They are called interaction pairs

Newton’s third law

- Why action and reaction forces don’t cancel each others?

In contrast to newton’s first law where balanced forces are exerted on the same system, in this case action and reaction forces are exerted on two different systems.

Solve p:104 sample problem

Wrap up & Closure

• Revising the main points seen this lesson.• Homework : Solve the practice sheet• SWQ2: Tuesday February 28th, 2012.Study from p:87-103 + worksheet+ quizzes+ notes on the copybook