Download Chapter M2

Chapter M2
Section 2 Newton’s Laws of Motion
Bellringer
If you are sitting still in your seat on a bus that is
traveling 100 km/h on a highway, is your body at rest
or in motion? Explain your answer. Use a diagram if it
will help make your answer clear.
Record your response in your science journal.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s First Law of Motion
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 describes the motion of
an object that has a net force of 0 N acting on it.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s First Law of Motion, continued
• Part 1: Objects at Rest Objects at rest will stay at
rest unless they are acted on by an unbalanced force.
• Part 2: Objects in Motion Objects will continue to
move with the same velocity unless an unbalanced
force acts on them.
• The image on the next slide shows how you can have
fun with Newton’s first law.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s First Law of Motion, continued
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s First Law of Motion, continued
• Friction and Newton’s First Law Friction between
an object and the surface it is moving over is an
example of an unbalanced force that stops motion.
• Inertia and Newton’s First Law Newton’s first law
is sometimes called the law of inertia. Inertia is the
tendency of all objects to resist any change in motion.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s First Law of Motion, continued
• Mass and Inertia Mass is a measure of inertia. An
object that has a small mass has less inertia than an
object that has a large mass.
• So, changing the motion of an object that has a small
mass is easier than changing the motion of an object
that has a large mass.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s Second 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.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s Second Law of Motion, continued
• 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.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s Second Law of Motion, continued
• Expressing Newton’s Second Law Mathematically
The relationship of acceleration (a) to mass (m) and
force (F) can be expressed mathematically with the
following equation:
a =
F
, or F = m  a
m
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s Second Law of Motion, continued
Click below to watch the Visual Concept.
Visual Concept
You may stop the video at any time by pressing
the Esc key.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
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.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s Third Law of Motion, continued
• Force Pairs Do Not Act on the Same Object A
force is always exerted by one object on another
object. This rule is true for all forces, including action
and reaction forces.
• Action and reaction forces in a pair do not act on the
same object. If they did, the net force would always be
0 N and nothing would ever move!
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s Third Law of Motion, continued
• All Forces Act in Pairs—Action and Reaction
Newton’s third law says that all forces act in pairs.
When a force is exerted, there is always a reaction
force.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 2 Newton’s Laws of Motion
Newton’s Third Law of Motion, continued
• The Effect of a Reaction Can Be Difficult to See
When an object falls, gravity pulls the object toward
Earth and pulls Earth toward the object.
• You don’t notice Earth being pulled upward because
the mass of Earth is much larger than the mass of the
object. Thus, the acceleration of Earth is much smaller
than the acceleration of the object.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 3 Momentum
Bellringer
Make a list of five things that have momentum and a
list of five things that don’t have momentum.
Explain your answer in your science journal.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 3 Momentum
Momentum, Mass, and Velocity
• The momentum of an object depends on the object’s
mass and velocity.
• Calculating Momentum The relationship of
momentum (p), mass (m), and velocity (v) is shown in
the equation below:
p=mxv
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 3 Momentum
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 3 Momentum
The 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.
• Objects Sticking Together After two objects stick
together, they move as one object. The mass of the
combined objects is equal to the masses of the two
objects added together.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 3 Momentum
The Law of Conservation of Momentum,
continued
• 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.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 3 Momentum
The Law of Conservation of Momentum,
continued
• Objects Bouncing Off Each Other When two
objects bounce off each other, momentum is usually
transferred from one object to the other.
• The transfer of momentum causes the objects to
move in different directions at different speeds.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter M2
Section 3 Momentum
The Law of Conservation of Momentum,
continued
• Conservation of Momentum and Newton’s Third
Law Conservation of momentum can be explained
by Newton’s third law.
• Because action and reaction forces are equal and
opposite, momentum is neither gained or lost in a
collision.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.