Newton’s First Law of Motion

Unit 2: Forces and Motion

Observation

• I place 3 washers on top of a toy car. I am going to push the toy car into a book on the table.

• What will the motion of the toy car be when it collides with the book?

• What will the motion of the washers be when the toy car collides with the book?

Why?

• Why did the car stop moving? • Why did the washers fall forward?

Newton’s First Law of Motion

• An object in motion stays in motion, an object at rest stays at rest UNLESS acted on by an UNBALANCED force.

• Objects with a constant velocity or no motion have zero net (balanced) force acting on them. – Example: • Waking up in the morning • Air hockey table

Inertia (In-ER-sha)

• Describes the resistance of an object to change its motion. – It is directly related to the objects mass

• Example: Two boxes are sitting at rest on the floor. They want to remain at rest. Which box will be easier to move?

a. 20 g b. 200 g

Explain this:

• When you’re standing in the Metro train, and it arrives at the next station by stopping very quickly.

• Why does the train stop? (it was in motion) • What happens to you? • Why do you fall forward a little bit when the

train stops?

Explain this:

• When you’re standing in the Metro train, and it arrives at the next station by stopping very quickly.

• Why does the train stop? (it was in motion) – An unbalanced force acted upon the train (brakes)

• What happens to you? – you fall forward as the train stops

• Why do you fall forward a little bit when the train stops? – Because you were in motion with the train and you stayed

in motion because there was no unbalanced force acting on you.

What happens here?

• You are in the car cruising at 40m/s. The driver hits the brakes suddenly.

• What is your initial motion when the brakes are hit?

• What keeps you from continuing to move forward? (you are a safe passenger)

What happens here?

• You are in the car cruising at 40m/s. The driver hits the brakes suddenly.

• What is your initial motion when the brakes are hit? – You begin to fly forward in the car because you were

in motion and wanted to stay in motion. • What keeps you from continuing to move

forward? (you are a safe passenger) – You are stopped from moving forward because you

were acted upon by an unbalanced force, the seatbelt

Think-Write-Pair-Share• In the next slide – I will ask you to describe what

is going on in the series of pictures. • Think – think about how Newton’s First Law

describes what is going on in the picture• Write – write down 1 sentence description of

each of the pictures • Pair – Pair with the student sitting next to you

and discuss your answers/opinion• Share – Share out with the class what you and

your partner came up with as your answers.

Final Test• Describe what is happening in each of these pictures

A)

B)

C)

Inertia (in-ER-sha) Practice

Which object has a greater inertia? The car or the person flying out of it? Why?

Which one will require a GREATER unbalanced force to stop its motion? The car or the person flying out?

Inertia (in-ER-sha) Practice

Which object has a greater inertia? The car or the person flying out of it? Why? The car because it has a greater mass.

Which one will require a SMALLER unbalanced force to stop its motion? The car or the person flying out? The person because it has a smaller mass.

Homework:

• Review pages 345-351• Page 351, #1-6

Have a nice day!