Newton's Laws of Motion

Newton's First Law of
Motion and Inertia

Unit: 7

Lesson:18

01.

What is inertia, and how does it affect the motion of an object?

Essential Questions

LEARNING
OBJECTIVES

Describe Newton's First Law of Motion as it relates to
inertia.

Practice or Check

•

Which line on the graph below represents the fastest moving object?

How about the slowest?

Discussion

Imagine that you’re riding in a car and the driver suddenly puts on the brakes. The car stops, but your body seems to keep going! You slide forward in your seat until your seatbelt catches you and holds you back.

Why do you think this happens? Discuss with a partner and record your answer on your Guided Notes page.

Be prepared to discuss!

Open Ended

Why do you continue to move forward?

PHYSICAL SCIENCE | LESSON 7.18 | NEWTON'S FIRST LAW OF MOTION AND INERTIA

Discussion

7

If you and your partner said that the passenger keeps moving forward even as the car slows and stops…you are correct!

Listening Activity

The science behind this phenomena was discovered by Sir Isaac
Newton.
Newton described 3 laws of motion that can be used to explain the movement of objects around us.
Watch this short video shared by your teacher to learn more about him!

Notes

Newton’s 1st Law of Motion

(Law of Inertia)

The velocity of an object will remain
constant unless a net force acts on it.

An object at rest will stay at rest, and an object in motion will stay in motion unless acted upon by an outside force.

Notes

Newton’s 1st Law of Motion

(Law of Inertia)

Basically, an object will keep doing what it was
doing” in the same direction at the same
speed unless acted on by an unbalanced
force.

If the object was sitting still, it will remain
stationary. If it was moving at a constant
velocity, it will keep moving.

It takes force to change the motion of an object.

Notes

Inertia: the tendency of an object to resist changes in its state of motion. The First Law states that all objects have
inertia.

The more mass an object has, the more
inertia it has (and the harder it is to change its motion).

Newton’s 1st Law of Motion

(Law of Inertia)

Example 1

The two trucks are traveling at a constant 15 mph. They then put the trucks into neutral and coast. The vehicle on the right is filled with dirt:

Which truck will stop first: heavy or light truck?

Draw

Which truck will stop first? Heavier or lighter

PHYSICAL SCIENCE | LESSON 7.18 | NEWTON'S FIRST LAW OF MOTION AND INERTIA

Example 1

13

The two trucks are traveling at a constant 15 mph. They then put the trucks into neutral and coast. The vehicle on the right is filled with dirt:

Which truck will stop first: heavy or light truck?

Example 2

If an elephant were chasing you, its enormous mass would be most threatening. But if you zigzagged, its mass would be to your advantage.
Why?

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Name one important thing you learned in class today.

Newton's 2nd Law of Motion

Unit: 7

Lesson:19

01.

How does the applied force to an object and its
mass effect that object's acceleration?

Essential Questions

LEARNING
OBJECTIVES

Describe and calculate the relationship between force,
mass, and acceleration.

Let’s Summarize

Explain the function of airbags and seat belts in a car in
terms of Newton’s 1st Law of Motion.

Open Ended

What is the purpose of airbags and seatbelts?

PHYSICAL SCIENCE | LESSON 7.19 | NEWTON'S 2ND LAW OF MOTION

Notes

7

Newton’s
Second
Law of
Motion

An object’s acceleration depends on:
•the strength of the unbalanced force acting on it
•the mass of the object

a=F

m

force

mass

acceleration

F =ma
More commonly written
as:

PHYSICAL SCIENCE | LESSON 7.19 | NEWTON'S 2ND LAW OF MOTION

Example 1

Pull on each wagon as hard as you can, applying the same force, the
one with less mass will have greater acceleration!

F=ma

8

PHYSICAL SCIENCE | LESSON 7.19 | NEWTON'S 2ND LAW OF MOTION

Example 1

What would have to change to get the greater mass to accelerate at
the same rate as the lesser mass?

9

F=ma

PHYSICAL SCIENCE | LESSON 7.19 | NEWTON'S 2ND LAW OF MOTION

Example 1

MORE MASS NEEDS MORE FORCE FOR GREATER ACCELERATION!

10

F=ma

PHYSICAL SCIENCE | LESSON 7.19 | NEWTON'S 2ND LAW OF MOTION

Example 2

F=ma

Newton’s 2nd Law proves that different masses accelerate to the earth
at the same rate, but with different forces.

• We know that objects with

different masses accelerate to
the ground at the same rate.

• However, because of the 2nd

Law we know that they don’t hit
the ground with the same force.

F = ma

98 N = 10 kg x 9.8 m/s/s

F = ma

9.8 N = 1 kg x 9.8 m/s/s

11

PHYSICAL SCIENCE | LESSON 7.19 | NEWTON'S 2ND LAW OF MOTION

Practice or Check

12

1. What acceleration will result when a 12-N net force applied to a
3-kg object? A 6-kg object?

2. A net force of 16 N causes a mass to accelerate at a rate of 5
m/s2. Determine the mass.

3. How much force is needed to accelerate a 66-kg skier 1
m/sec/sec?

4. What is the force on a 1000-kg elevator that is falling freely at
9.8 m/sec/sec.?

F=ma

PHYSICAL SCIENCE | LESSON 7.19 | NEWTON'S 2ND LAW OF MOTION

Practice or Check

13

1. What acceleration will result when a 12-N net force applied to a

3-kg object? 4 m/s/s and 2m/s/s

2. A net force of 16 N causes a mass to accelerate at a rate of 5

m/s2. Determine the mass.3.2 kg

3. How much force is needed to accelerate a 66-kg skier 1

m/sec/sec?66 N

4. What is the force on a 1000-kg elevator that is falling freely at 9.8

m/sec/sec.?9800 N

F=ma

PHYSICAL SCIENCE | LESSON 7.19 | NEWTON'S 2ND LAW OF MOTION

Computer Activity

14

Your teacher will direct you to a computer lab activity to
practice what you have learned.

Let’s Summarize

PHYSICAL SCIENCE | LESSON 7.19 | NEWTON'S 2ND LAW OF MOTION

15

1. Newton’s second law can be written mathematically as:

_____________ = _____________ x _____________.

2. From Newton’s second law, an object’s acceleration
depends on the object’s _______ and the strength of the
___________ _____ acting on it.

3. Your _____________ will be different on other planets
because the acceleration due to gravity is different.

4. BONUS: What are some examples of engineering designs
that must consider Newton’s second law of motion?