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Newton’s
Three Laws
of Motion
Sir Isaac Newton
(January 1643 – March 1727)
Newton's laws of
motion are three physical
laws which provide
relationships between the
forces acting on a body
and the motion of the
body.
Newton’s First Law of Motion
An object at rest
will remain at
rest- unless acted
upon by an
outside force.
Newton’s First Law of Motion
An object in
motion will remain
in motion – unless
acted upon by an
outside force.
Newton’s First Law of Motion cont.
An object at rest remains at
rest, and an object in
motion remains in motion at
a constant speed and in a
straight line unless acted
on by an unbalanced force.
Newton’s First Law of Motion
Newton’s First Law of Motion
AKA The Law of Inertia
Inertia is a resistance to
change in motion.
Can You Explain…
Newton’s First Law of Motion
Demos
Newton’s First Law of Motion
An object at
rest will
remain at
rest…
Table Cloth Trick
Newton’s First Law of Motion
Can You Explain…
Newton’s First Law of Motion
An object in motion will
continue to move in a
straight line.
For Example…
Anti-Inertia Belts
Newton’s First Law of Motion
Better known
as “Seatbelts” !
Poor Baby Barbie
Newton’s First Law of Motion
http://www.physicsclassroom.com/mmedia/newtlaw
s/cci.cfm
Newton’s 2nd Law of Motion
The acceleration of an object depends on the
mass of the object and the amount of force
applied.
• Newton’s second law describes the motion
of an object when an unbalanced force acts
on the object.
Newton’s
nd
2
Law of Motion
This Law shows the
relationship between
mass, force, and
acceleration.
When a force is
applied to a mass, it
accelerates.
The larger the mass of an
object, the more force needed
to start it, stop it, or change its
direction.
nd
2
Newton’s Law of Motion
Force = mass x acceleration
A speeding bullet and a slow moving train
both have tremendous force. The force of
the bullet can be attributed to its incredible
acceleration while the force of the train
comes from its great mass.
Newton’s
nd
2
Law of Motion
The acceleration of an object depends on the mass of
the object and the amount of force applied.
• Newton’s second law describes the motion of an
object when an unbalanced force acts on the object.
Newton’s
nd
2
Law of Motion
• Part 1: Acceleration Depends on Mass The
acceleration of an object decreases as its mass
increases. Its acceleration increases as its mass
decreases.
• Part 2: Acceleration Depends on Force An object’s
acceleration increases as the force on the object
increases. The acceleration of an object is always in
the same direction as the force applied.
Newton’s
nd
2
Law of Motion
Newton’s
nd
2
Law of Motion
For Example:
A Bowling Ball vs a
ping pong ball.
Choose Your Position..
Some Athletes are
long and lean, with
little body fat, and
little muscle.
Basketball players
and wide receivers
fit this category.
Newton’s
nd
2
Law of Motion
Newton’s
nd
2
Law of Motion
Choose Your Position…
Other athletes, on
the other hand, have
lots of body fat, lots
of muscle, and gain
weight easily.
Football lineman
and sumo wrestlers
are heavier and
rounder individuals
Momentum, Mass, and Velocity
• The momentum of an object is the product of the
object’s mass and velocity. Object at rest has zero
momentum.
Calculating Momentum The relationship of
momentum (p), mass (m) in kilograms, and velocity (v)
in meters per second, is shown in the equation below:
pmxv
What is
(i) the total kinetic energy before the collision;
(ii) the total kinetic energy after the collision.
(iii) the total loss in kinetic energy.
Momentum
Momentum
Law of Conservation of Momentum
• The law of conservation of momentum states that any
time objects collide, the total amount of momentum
stays the same.
Law of Conservation of Momentum
• The
combined objects have a different velocity
because momentum is conserved and depends
on mass and velocity.
• So, when the mass changes, the velocity must
change, too.
Law of Conservation of Momentum
• Objects Bouncing Off Each Other
When two objects bounce off each other,
momentum is transferred from one object to
the other.
• The transfer of momentum causes the
objects to move in different directions at
different speeds.
The Story of Fluffy
Newton’s First Law of Motion
Law of Conservation of Momentum
rd
& Newton’s 3 Law can be
explained…
Because action and reaction
forces are equal and opposite,
momentum is neither gained or
lost in a collision.
Forces Always Come in Pairs
.
Newton’s Third Law of Motion
Whenever one object exerts a force on a second
object, the second object exerts an equal and opposite
force on the first.
• Newton’s third law of motion can be simply stated as
follows: All forces act in pairs.
Newton’s

rd
3 Law
For every action force,
there is an equal, but
opposite, reaction
force.
http://science.discovery.com/interactives/literacy
/newton/newton.html
of Motion
The Action Force is Equal in
size but Opposite in Direction.
Action and Reaction forces
always act on different
objects.
Action Force: The man
pushes against the
wall.
Reaction Force: the wall
pushes on the man.
Newton's third law does not mean that forces always cancel out
so that nothing can ever move. If these two figure skaters,
initially at rest, push against each other, they will both move.
Another example: Recoil of a
gun or cannon
Or…Launching a Rocket

Or… a Lawn Sprinkler