Transcript Newton`s Laws of Motion

Set your stuff
down, get ready
to go to the
media center for
first part of class
WHAT IS A FORCE?.
Force- Definition
A push or pull in a
direction
Characteristics of Forces
•
•
•
•
Forces are measured in Newtons (N)
They usually work in pairs
Have a direction
Affect motion
Types of Forces
•
•
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Gravity
Friction
Magnetic
Elastic
Applied Force
How do Forces act on
Objects? Force Diagrams
Normal
force (force of
ground/Earth)
friction
gravity
Force Diagrams
“free fall”
friction
(air resistance)
gravity
Force Diagram
Normal
force (force of
friction
gravity
slide/Earth)
Force Diagrams
Normal
force (force of
ground/Earth)
friction
gravity
Applied
(guy
pushing)
Net Force
Net Force = The sum of all
the forces on an object
• Same direction, add
20+10=30N
• Opposite direction, subtract
(bigger one wins)
20-10= 10N
STOPPED HERE ON FEB 11
Newton’s
Laws of
Motion
I. Law of Inertia
II. F=ma
III. Action-Reaction
Newton’s 3 Laws of Motion
While some people know what
Newton's laws say, many
people do not know what they
mean (or simply do not
believe what they mean).
1st Law of Motion
(Law of Inertia)
Objects will stay at rest, or
stay in motion until an outside
force acts on it.
1st Law

Inertia the
tendency of an
object to resist
changes in
motion
The more mass, the more
inertia something has
1st Law

Unless acted
upon by an
unbalanced
force, this golf
ball would sit on
the tee forever.
1st Law

Once flying in
the air, if an
unbalanced force
wasn't applied
(such as gravity
or air friction), it
would never
stop!
Question
Why then, do we observe every
day objects in motion slowing
down and becoming motionless
seemingly without an outside
force?
FRICTION!!
Objects on earth, are under
the influence of friction.
(friction from the air, friction
when rolling on a surface,
friction when sliding)
Newtons’s 1st Law and You
Don’t let this be you. Wear seat belts!
Because of inertia, objects (including you) resist
changes in their motion. When the car going 80
km/hour is stopped by the brick wall, your body
keeps moving at 80 m/hour.
Newton's 2nd Law
2nd Law
The net force of an object
is equal to the product of its
mass and acceleration, or
F=ma.
Force = Mass x Acceleration
Newton's 3rd Law

For every action, there is an
equal and opposite reaction.
When you sit in your chair, your
body exerts a downward force on
the chair and the chair exerts an
upward force on your body.
3rd Law
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.


3rd Law
Think of a car moving
forward.....
Which direction do the
wheels move against the
road in the picture below??
Car moving this way