NEWTON’S
LAWS OF
MOTION
1. The Law of Inertia
2. F=ma
3. Action & Reaction
Newton’s Laws of Motion

1st Law – An object at rest will stay at rest, and an
object in motion will stay in motion at a constant
velocity, unless acted upon by an another force.
2nd Law – Force equals mass times acceleration.
 3rd Law – For every action there is an equal and

opposite reaction.
1st Law of Motion
The Law of Inertia
An object at rest will stay at
rest, and an object in motion
will stay in motion at constant
velocity, unless acted upon by
an unbalanced force.
Inertia is
the
tendency of
an object to
resist
changes in
its velocity.
These basketballs will not move
unless acted on by a force.
1st Law- Inertia
1st Law

Once a force
actied on it motion-it would
never stop!!
~ unless acted on
by a force (push,
pull, gravity, air or
friction)
1st Law

Unless acted
upon by an
unbalanced
force, this golf
ball would sit on
the tee forever.
…BUT…
F
R
I
C
T
I
O
N
Why do we observe every
day objects in motion,
slowing down and
eventually stopping without
an outside force acting on
them?
It’s a force we sometimes cannot
see…
ALL objects on earth are
under the influence of friction.
Unlike the
frictionless
space the moon
travels
through.
Let’s review friction…
Friction is…


The force that two
surfaces exert on each
other when they rub
against each other.
It depends on…
1. How hard the surfaces
push
2. The types of surfaces
The 4 types of friction:




Static Friction
Sliding Friction
Rolling Friction
Fluid Friction
Slide your book across your desk gently
and watch it come to a stop. WHY?

The book comes to a
rest because a force
was exerted on it friction - which brings
the book to a rest.
According to Newton’s 1st law, the
book would continue in motion at
the same speed and direction forever! (Or at least to the end of the
desk.) if it wasn’t for that
unbalanced force acting on itFRICTION!!!
Newtons’s
st
1
Law and You
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.
Don’t let this be you!
Wear seat belts.
Mass Matters!!!

The greater the mass an object has, the more force
it will take to put the object in motion- therefore it
will have a greater inertia
Newton’s second law says that the amount
of acceleration needed to make an object
change its motion depends on the MASS of
the object and the net force required.
SOOO…if you want to find force:
Force= mass x acceleration
The
nd
2
Law
2nd Law

Lets try it out!
How much force is needed to accelerate a 1400
kilogram car 2 m/s2?
Write the formula
F= M x A
Fill in the formula. (Don’t forget units!!!)
F= 1400kg x 2m/s/s
Solve the formula.
2800 N
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
F = ma
98 N = 10 kg x 9.8 m/s/s
9.8 N = 1 kg x 9.8 m/s/s
For every action there is
an equal and opposite
reaction.
Newton’s 3rd Law
3rd Law
Its BALANCED!!
According to Newton,
whenever two objects
interact with each other,
they exert forces on
each other. 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
There are two forces
resulting from this
interaction - a force on
the chair and a force on
your body. These two
forces are called action
and reaction forces.
Newton’s 3rd Law in Nature


Think about a fish swimming
through water. A fish uses its
fins to push water
backwards. In turn, the
water reacts by pushing the
fish forward, moving the fish
through the water.
The size of the force on the
water equals the size of the
force on the fish; the
direction of the force on the
water (backwards) is
opposite the direction of the
force on the fish (forwards).
Other examples of Newton’s Third
Law

The baseball forces the
bat to the left (an
action); the bat forces
the ball to the right (the
reaction).
3rd Law

Think about your car or
bus ride on the way to
school. Both are
equipped with wheels
which spin backwards.
As the wheels spin
backwards, they grip the
road and push the road
backwards.
Momentum
…IT’S THE
PRODUCT OF
MASS AND
VELOCITY
The unit is….
Kg × m/s
WITH A
DIRECTON
Momentum =
mass × VELOCITY
If a small object is traveling at a high speed it can have
more momentum that a more massive object traveling at
a lower speed.
MASS MATTERS!!
The Law of Conservation of Momentum



In the absence of outside forces, the total momentum
of objects that interact DOES NOT CHANGE
What outside forces?!?
Gravity and FRICTION!!!
Movements in Momentum
Conserving Momentum

The total momentum of any
group of object remains the
same, or is conserved, unless
an outside force acts on the
objects.
FRICTION!!!
Transferring Momentum


It is a type of conservation
of momentum.
Momentum can be
transferred from one object
to another
Collision with 2 moving objects
2m/s
4m/s
4m/s
2m/s
Collisions with 1 moving object
0m/s
4m/s
When the blue car hits the yellow car, it will transfer its momentum
to that car.
The yellow car would move at 4m/s and the blue car would be at
rest.