Newton’s First Law of Motion:The Law of Inertia

Physics

Oct 12/15

Chapter 4

Kena Allison

What is Newton’s 1st Law

Topic

Newton’s 1st Law

Facts• Also called the Law of

inertia• Every object continues

in a state of rest, or motion in a straight line at constant speed, unless it is compelled to change that state by nonzero forces exerted upon it.

So What?

TopicPut Newton’s 1st Law

into your own words

FactsObjects in motion stays

in motion in a straight line and with the same speed AND objects at rest stay at rest unless an outside force acts upon it.

Why is it called the Law of Inertia?

Topic• inertia

Facts• Property of a body/object

to resist change • Think of it as an object’s

laziness– If an object is at rest, then it is

too “lazy” to move– If an object is in motion, then it

is too “lazy” to stop

• Mass is how we measure inertia (kg)

Do you get the joke?

Get It?!

A video on the 1st Law

• Newton's First Law Explained

Let’s take a closer look at mass

Topic• mass

Facts• The amount of

matter/inertia an object has

• If an object has more mass, then it has more inertia (more laziness)

• Symbol is m• The units are kilograms

(kg)

Now Apply These Concepts

TaskExplain how a table

cloth can be removed from under a plate without the plate moving

ExplanationThe plate does not move

because it has inertia and according to Newton’s 1st Law since the plate is at rest, it wants to stay at rest. The outside force is only applied to the cloth, not the plate.

What might cause an object to change its state?

Topic

• ForceFacts

• Any push or pull

• Vector quantity

• Symbol is F

• Units are Newtons (N)

Different Types of Forces

Forces

Friction Force Net ForceNormal/

Support Force

Ff FNet FN

weight

w

Reach for the Stars

• What are the units for friction force?

Newtons (N)

All forces have Newtons (N) as their units

What might cause an object to change its state?

Topic

Friction Force

Facts• Force that acts between

materials that touch as they move past each other that SLOWS or STOPS MOTION.

• Caused by irregularities in surfaces of objects that are touching

What might cause an object to change its state?

Topic

Net Force

Facts• The combinations of forces

being applied• Show with vectors

Equilibrium Rule

• When the net force is zero, an object is in equilibrium

• No motion (static equilibrium)• Motion in straight line with constant speed

(dynamic equilibrium)

Let’s Take a Closer Look at a specific type of Force

Topic

Normal forceFacts• Also called support force• Upward Force • Opposite force of gravity

Let’s Take a Closer Look at a specific type of Force

Topic

weightFacts• The force of gravity on

an object • WEIGHT IS NOT

MASS!!!• Weight equals mass

times gravity • w = mg

Newton’s 1st Law Relates to Real-World Safety

• Seatbelts and Headrest

Closing

Task

According to the law of inertia, why is it important to have seatbelts in cars?

Why headrest?

Explanation