Download Gravity and Motion

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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Quick Write
Do you know of a place where gravity does not exist?
If so, where? Why or why not?
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Chapter 13
Section 1 Gravity: A Force of
Attraction
What You Will Learn
• Gravity affects all matter.
• Gravity is a force.
• The law of universal gravitation explains how
distance, mass, and gravitational force are related.
• Weight depends on gravity, but mass does not.
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Multiple Meanings
Term
Common Meaning
Scientific Meaning
law
rule from government
description that
predicts what will
happen if something
specific happens
vacuum
electric appliance that
sucks up small things
a place with no matter
(objects)
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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.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
The Effects of Gravity on Matter
• 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
• Gravity between the objects of the solar system holds the solar
system together.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
The Effects of Gravity on Matter
• Earth has a huge mass. Therefore, Earth has
strong gravitational force.
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Sir Isaac Newton
• a British scientist
• Discovered the law
of universal
gravitation in1665.
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Law of Universal Gravitation (Newton)-General
• The same unbalanced force
that affects the motion of
small objects (apple) also
affects the motion of larger
objects (moon).
• This unbalanced force =
gravity.
• universal = applies to all
objects in the universe
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Law of Universal Gravitation (Newton)-Mass
• All objects in the universe attract each other through
gravitational force.
• mass of objects =
gravity between objects
• mass of objects = gravity between objects
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Activity:
Mass Judgments
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Law of Universal Gravitation (Newton)-Distance
• The force of gravity depends on the distance
between two objects.
• distance = force of gravity
• distance = force of gravity
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Law of Universal Gravitation (Newton)-Solar System
• 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 = the gravitational
force on an object
• SI unit of force = newton (N).
• Weight can change with the
location of the object in the
universe.
• spring scale
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Chapter 13
Section 1 Gravity: A Force of
Attraction
Mass and Gravitational Force
•
•
•
•
Mass = the amount of matter in an object
kilograms (kg) or grams (g)
Mass does not change when gravitational force changes.
balance scale
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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.
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Lab:
Mass and Weight
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End of Section 1
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Gravity and Motion (Ch. 13, Sect. 2)
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Chapter 13
Section 2 Gravity and Motion
What You Will Learn
• acceleration due to gravity
• air resistance
• projectile motion: horizontal motion and vertical
motion.
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Why It Matters
• Gravity affects the motion of everything that you drop
or throw.
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BrainPop:
Acceleration
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Chapter 13
Section 2 Gravity and Motion
Gravity and Falling Objects
• Acceleration = change in velocity over time
• Review: velocity = change in speed and/or direction
weight = gravitational force (unbalanced)
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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 force of gravity is the same for all objects near
Earth’s surface.
• Acceleration =
9.8 m/s2
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Gravity and Falling
Objects:
Show these forces,
using vectors, on
graph paper.
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Calculating the Change in Velocity
• Formula: Δv = g x t
• Δv = change in velocity
• g = acceleration due to gravity (always 9.8 m/s)
• t = time object falls (seconds)
 Change in Velocity: Δv = 9.8 m/s x total seconds
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Change in Velocity: Math Practice
formula:
Δv = 9.8 m/s x total seconds
Δv =
Δv =
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Video Clip:
The Physics of Skydiving
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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.
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Chapter 13
Section 2 Gravity and Motion
Air Resistance and 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
Show these forces, using vectors, on graph
paper:
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Chapter 13
Section 2 Gravity and Motion
Air Resistance and Falling Objects
• An object falls at its
terminal velocity
when the upward
force of air
resistance equals
the downward force
of gravity.
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Chapter 13
Section 2 Gravity and Motion
Air Resistance and Falling Objects
• An object is in free
fall if gravity is the
only force acting on
it.
• It can only happen
in a vacuum or
outer space, where
there’s no air.
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Lab:
Parachutes and Air Resistance
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Projectile Motion and Gravity
• vertical motion: gravity
accelerates at 9.8 m/s2
(if air resistance is
ignored).
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Projectile Motion and Gravity
• horizontal motion: not affected by gravity
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Chapter 13
Section 2 Gravity and Motion
Projectile Motion and Gravity
• horizontal movement + vertical movement
= a curved path
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Chapter 13
Forces and Motion
Show these forces, using vectors, on graph
paper:
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Poster Project:
Projectile 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.
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Chapter 13
Section 2 Gravity and Motion
Orbiting and Gravity
• 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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BrainPop:
Space Flight
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Chapter 13
Forces and Motion
Show these forces, using vectors, on graph
paper:
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Chapter 13
Section 2 Gravity and Motion
• The path of an orbiting
object is not quite a
circle. Instead, the
path is an ellipse.
Orbiting and Gravity
• 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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Lab:
Circling Marbles
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Chapter 13
Section 2 Gravity and Motion
• Gravity helps maintain
the shape of the solar
system by keeping
large objects such as
the planets in their orbit
around the sun.
Orbiting and Gravity
• 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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End of Section 2
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Chapter 13
Section 3 Newton's Laws of
Motion
What You Will Learn
Newton’s three laws of motion
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s First Law
• An object at rest will remain
at rest unless acted upon by
an unbalanced force.
• An object in motion will
remain in motion at a
constant speed and in a
straight line unless acted
upon by an unbalanced
force.
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Newton’s First Law
• Friction makes Newton’s first law difficult
• aka “law of inertia”
• mass is a measure of inertia.
– small mass = less inertia
– large mass = more inertia
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s Second Law of Motion
• Acceleration of an object depends on the mass and
the amount of force.
• greater mass = greater the force needed
• greater force = increase in acceleration
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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
• All forces act in pairs.
• When a force is exerted, there is always an equal and opposite
reaction force.
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Chapter 13
Section 3 Newton's Laws of
Motion
Newton’s First Law
• PBS Teachers — Resources For The Classroom
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End of Section 3
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