Transcript Chapter 13 ppt

Chapter 13
Forces and Motion
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Section 1 Gravity: A Force of Attraction
Section 2 Gravity and Motion
Section 3 Newton's Laws of Motion
Concept Map
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Bellringer
Recall pictures or videos you have seen showing
astronauts under “weightless” conditions in space.
Try to imagine what it would be like to live your daily
life in weightless conditions.
In your Science Journal, write one or two paragraphs
explaining how you would carry out daily activities
while weightless. Describe eating, sleeping, going to
school, working in class, and any other activity you
would like to include.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
What You Will Learn
• Gravity affects all matter, including the parts of the
solar system.
• Because gravity is a force, it can change the velocity
of objects.
• The law of universal gravitation explains how
distance, mass, and gravitational force are related.
• The weight of an object depends on gravity, but the
mass of the object does not.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
The Effects of Gravity on Matter
• Gravity is a force of attraction between objects that is
due to their masses.
• All matter has mass. Gravity is a result of mass.
Therefore, all matter is affected by gravity.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
The Effects of Gravity on Matter, continued
• Gravity between the objects of the solar system holds
the solar system together.
• Compared with all objects around you, Earth has a
huge mass. The gravitational attraction of Earth is
thus an important force that you experience all the
time.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Newton and the Study of Gravity
• Newton concluded that the same unbalanced force
that affects the motion of small objects, such as an
apple, also affects the motion of larger objects, such
as the moon.
• Newton called this unbalanced force gravity.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Newton and the Study of Gravity, continued
• Newton summarized his ideas about gravity in the
law of universal gravitation.
• This law is called universal because it is thought to
apply to all objects in the universe.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
The Law of Universal Gravitation
• The law of universal gravitation states that all objects
in the universe attract each other through
gravitational force.
• The gravitational force between objects depends on
the product of the masses of the objects. So, the
gravity between objects increases as the masses of
the objects increases.
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Chapter 13
Forces and Motion
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Chapter 13
Section 1 Gravity: A Force of
Attraction
The Law of Universal Gravitation, continued
• The force of gravity depends on the distance
between two objects.
• As the distance between two objects gets larger, the
force of gravity gets much smaller.
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Chapter 13
Forces and Motion
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Chapter 13
Section 1 Gravity: A Force of
Attraction
The Law of Universal Gravitation, continued
• The gravitational force of the sun affects the
movement of all the planets. This force helps them
stay in orbit around the sun.
• So, the force of gravity has an important role in
maintaining the shape of the solar system.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Weight and Gravitational Force
• Weight is related to mass, but they are not the same.
Weight is a measure of the gravitational force on an
object.
• Weight is expressed in the SI unit of force, the
newton (N).
• The value of an object’s weight can change with the
location of the object in the universe.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Weight and Gravitational Force, continued
• Mass is a measure of the amount of matter in an
object. Mass is usually expressed in kilograms (kg) or
grams (g).
• An object’s mass does not change when gravitational
force changes.
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Chapter 13
Forces and Motion
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Gravity and Static Objects
• Gravity also acts on nonmoving, or static, objects.
• Gravity is often balanced by elastic forces due to
tension or compression.
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Chapter 13
Section 2 Gravity and Motion
Bellringer
Imagine holding your arm straight out from your
shoulder. A solid ball is in your hand. Then, you drop
the ball and watch it as it falls. What force causes the
ball to fall to the ground?
In your Science Journal, write one or two sentences
describing the motion of the ball as it falls. Describe
the direction of motion and tell whether the ball falls
at a constant velocity or whether its velocity changes.
Remember that the ball is not moving until you let go.
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Chapter 13
Section 2 Gravity and Motion
What You Will Learn
• The acceleration due to gravity is the same for all
objects near Earth’s surface.
• Air resistance is a force that opposes the motion of
objects through air.
• Projectile motion has two components—horizontal
motion and vertical motion.
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Chapter 13
Section 2 Gravity and Motion
Gravity and Falling Objects
• All objects fall to the ground at the same rate
because the acceleration due to gravity is the same
for all objects near Earth’s surface.
• Acceleration is the rate at which velocity changes
over time.
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Chapter 13
Section 2 Gravity and Motion
Gravity and Falling Objects, continued
• An object accelerates when the forces on it are
unbalanced.
• Gravity exerts a downward, unbalanced force on
falling objects. So, falling objects accelerate.
• Falling objects accelerate toward Earth at a rate of
9.8 m/s2.
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Chapter 13
Forces and Motion
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Chapter 13
Section 2 Gravity and Motion
Air Resistance and Falling Objects
• Air resistance is the force that opposes the motion of
objects through air. Air resistance slows the
acceleration of falling objects.
• The amount of air resistance acting on a falling object
depends on the size, shape, and speed of the object.
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Chapter 13
Forces and Motion
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Chapter 13
Section 2 Gravity and Motion
Air Resistance and Falling Objects, continued
• An object falls at its terminal velocity when the
upward force of air resistance equals the downward
force of gravity.
• An object is in free fall if gravity is the only force
acting on it.
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Chapter 13
Section 2 Gravity and Motion
Air Resistance and Falling Objects, continued
• Because air resistance is a force, free fall can
happen only where there is no air.
• The term vacuum is used to describe a place in
which there is no matter. Vacuum chambers are
special containers from which air can be removed to
make a vacuum.
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Chapter 13
Forces and Motion
Free Fall
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Chapter 13
Section 2 Gravity and Motion
Projectile Motion and Gravity
• Projectile motion is the curved path that an object
follows when thrown, launched, or otherwise
projected near the surface of Earth.
• Projectile motion is made of two different motions, or
movements: horizontal movement and vertical
movement. When these two movements are put
together, they form a curved path.
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Chapter 13
Section 2 Gravity and Motion
Projectile Motion and Gravity, continued
• Horizontal movement is movement parallel to the
ground.
• Gravity does not affect the horizontal movement of
projectile motion.
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Chapter 13
Section 2 Gravity and Motion
Projectile Motion and Gravity, continued
• Vertical movement is movement perpendicular to the
ground.
• Gravity affects the vertical movement of an object in
projectile motion by pulling the object down at an
acceleration of 9.8 m/s2 (if air resistance is ignored).
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Chapter 13
Forces and Motion
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Chapter 13
Section 2 Gravity and Motion
Orbiting and Gravity
• An object is orbiting when it is moving around another
object in space.
• The two movements that come together to form an
orbit are similar to the horizontal and vertical
movements in projectile motion.
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Chapter 13
Forces and Motion
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Chapter 13
Section 2 Gravity and Motion
Orbiting and Gravity, continued
• The path of an orbiting object is not quite a circle.
Instead, the path is an ellipse.
• Centripetal force is the unbalanced force that makes
objects move in an elliptical path.
• Gravity provides the centripetal force that keeps
objects in orbit.
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Chapter 13
Forces and Motion
Gravity and Orbit
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Chapter 13
Section 2 Gravity and Motion
Orbiting and Gravity, continued
• Gravity helps maintain the shape of the solar system
by keeping large objects such as the planets in their
orbit around the sun.
• Gravity also affects the movement of very small
objects in the solar system, such as the tiny particles
that make up the rings of Saturn.
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Chapter 13
Section 3 Newton's Laws of
Motion
Bellringer
Think of what forces you would feel in each of these two
scenes. Then, in your Science Journal, for each
scene, answer the two questions that follow each
scene.
Scene 1: You are sitting still in your seat on a bus
traveling straight ahead at a constant rate of speed.
Are the forces acting on your body balanced or
unbalanced? How do you know?
Scene 2: The driver suddenly applies the brakes, and the
bus slows down. Are the forces acting on your body
balanced or unbalanced? How do you know?
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Chapter 13
Section 3 Newton's Laws of
Motion
What You Will Learn
• Newton’s first law of motion states that the motion of
an object will change only if unbalanced forces act on
the object.
• Newton’s second law of motion states that the
acceleration of an object depends on the object’s
mass and on the force exerted on the object.
• Newton’s third law of motion states that whenever
one object exerts a force on a second object, the
second object exerts an equal and opposite force on
the first.
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s First Law
• Newton’s first law of motion states that the motion of
an object will not change if the forces on it are
balanced.
• Newton’s first law of motion describes the motion of
an object that has a net force of 0 N acting on it.
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s First Law, continued
• An object that is not moving is said to be at rest.
Objects at rest will not move unless acted upon by an
unbalanced force.
• Objects in motion will continue to move at a constant
speed and in a straight line unless acted upon by an
unbalanced force.
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s First Law, continued
• Friction is an unbalanced force that changes the
motion of objects.
• Because of friction, observing Newton’s first law is
often difficult.
• Newton’s first law of motion is sometimes called the
law of inertia.
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s First Law, continued
• Inertia is the tendency of an object to resist being
moved or, if the object is moving, to resist a change
in speed or direction until an outside force acts upon
the object.
• Mass is a measure of inertia. An object that has a
small mass has less inertia than an object that has a
large mass.
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Chapter 13
Forces and Motion
Newton’s First Law
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s Second Law of Motion
• Newton’s second law of motion states that 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.
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s Second Law of Motion, continued
• The greater the mass of an object is, the greater the
force needed to achieve the same acceleration.
• The acceleration of an object is always in the same
direction as the net force applied.
• An object’s acceleration increases as the force on the
object increases.
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Chapter 13
Forces and Motion
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s Third Law of Motion
• Newton’s third law of motion states that whenever
one object exerts a force on a second object, the
second object exerts an equal and opposite force on
the first object.
• All forces act in pairs. When a force is exerted, there
is always a reaction force.
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s Third Law of Motion, continued
• Action and reaction force pairs are present even
when there is no movement.
• A force is always applied by one object on another
object. However, action and reaction forces in a pair
do not act on the same object.
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Chapter 13
Forces and Motion
Action and Reaction Forces
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Chapter 13
Forces and Motion
Concept Map
Use the terms below to complete the concept map
on the next slide.
force
free fall
terminal velocity
gravity
air resistance
projectile motion
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Chapter 13
Forces and Motion
Concept Map
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Chapter 13
Forces and Motion
Concept Map
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