Download Chapter 2 - Forces In Motion

Chapter 6 - Forces In Motion
Section 2 – Newton’s Laws of
Motion
pp. 158 - 165
TERMS TO LEARN
Inertia – the tendency of all objects
to resist any change in motion
 Momentum – a property of a moving
object that depends on the object’s
mass and velocity.

NEWTON’S THREE LAWS OF
MOTION


In his book, Principia,
Newton described the
three laws of motion.
He did not discover all
three laws, he
explained them in a
way that many people
could understand
NEWTON’S FIRST LAW OF MOTION
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This is also known as the Law of Inertia
It says : An object in motion will remain
in motion at a constant speed and in the
same direction unless acted on by an
unbalanced force.
An object at rest will remain at rest unless
acted upon by an unbalanced force.
NEWTON’S FIRST LAW OF MOTION



In other words…
Unless you apply a force, things tend to
keep on doing what they were doing in
the first place.
Objects at rest (not moving) will not begin
moving unless a push or pull is exerted on
them.
NEWTON’S FIRST LAW OF MOTION
NEWTON’S FIRST LAW OF MOTION


An object moving at a certain velocity will
continue to move forever at that same
speed and in the same direction unless an
unbalanced force acts on it.
Inertia is related to mass. Mass is a
measure of inertia.
NEWTON’S FIRST LAW OF MOTION


An object with a small
mass has less inertia
than an object with a
large mass.
For example…
 A tractor trailer has
more mass than a
motorcycle
NEWTON’S FIRST LAW OF MOTION


How do ABS
(automatic brake
systems) work in
cars?
The system is
controlled by a
computer that
prevents skidding by
sensing when the
wheels are about to
lock.
ABS BRAKES EXPLAINED

The computer
releases and reapplies
the brakes up to 25
times a second.
Instead of skidding
out of control, the car
slows down and stops
safely.
NEWTON’S SECOND LAW OF
MOTION
The acceleration of an object
depends on the mass of the object
and the amount of force applied to it.
 Equation: F = m∙a
 Force = mass times acceleration

NEWTON’S SECOND LAW OF
MOTION

Acceleration depends on force.
Acceleration and force are directly
proportional. This means as force
increases acceleration also increases
and vice versa.
NEWTON’S SECOND LAW OF
MOTION



Acceleration also depends on mass.
Acceleration and mass are inversely
proportional. This means as mass
increases, acceleration decreases and vice
versa.
Remember that mass is also a measure of
an object’s inertia.
Complete Math Focus on p. 162 of text.
NEWTON’S SECOND LAW OF
MOTION

In other words…
 Force causes an object to
accelerate, while the object’s mass
resists the acceleration.
 The larger the object (the more
mass it has), the harder it is to
accelerate.
NEWTON’S THIRD LAW OF
MOTION

Whenever one object exerts a force
on a second object, the second object
exerts a force that is equal in size and
opposite in direction on the first
NEWTON’S THIRD LAW OF
MOTION
In other words…
 For every action there is an equal and
opposite reaction.

NEWTON’S THIRD LAW OF
MOTION
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All forces act in pairs called action-reaction
force pairs
If a force is exerted, another force occurs
that is equal in size and opposite in
direction to the first.
ACTION-REACTION FORCE PAIRS DO NOT
ACT ON THE SAME OBJECT! See Figure 7
& Figure 8 on p. 164.
MOMENTUM

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Momentum is a property of a moving
object that depends on its mass and
velocity.
The more momentum an object has, the
harder it is to stop the object or change its
direction.
MOMENTUM
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Equation for Momentum –
p = m∙v
Where p = momentum, m= mass and v =
velocity