Transcript forces and motion notes

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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Module M: Chapter 2
Forces and Motion
Section 1: Gravity and Motion
Section 2: Newton’s Laws of Motion
Section 3: Momentum
End of Slide
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 1
Gravity and Motion
Bellringer
Answer the following question in your science journal:
If Wile E. Coyote and a boulder fall off a cliff at the same
time, which do you think will hit the ground first? Would it
matter if the cliff were very high or particularly low? How
could Mr. Coyote slow down his fall?
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 1
Gravity and Motion
Objectives
• Explain the effect of gravity and air resistance on falling
objects.
• Explain why objects in orbit are in free fall and appear to
be weightless.
• Describe how projectile motion is affected by gravity.
End of Slide
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 1
Gravity and Motion
Gravity and Falling Objects
• Gravity and Acceleration Objects fall to the ground at
the same rate because the acceleration due to gravity is
the same for all objects.
• Acceleration Due to Gravity As shown on the next slide,
for every second that an object falls, the object’s downward
velocity increases by 9.8 m/s.
• Velocity of Falling Objects Velocity equals gravity times
time.
End of Slide
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Section 1
Falling Objects Accelerate at a Constant Rate
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Section 1
Gravity and Motion
Air Resistance and Falling Objects
• Acceleration Stops at Terminal Velocity As the speed
of a falling object increases, air resistance increases. The
upward force of air resistance continues to increase until it
is equal to the downward force of gravity. The object then
falls at a constant velocity called the terminal velocity.
• Free Fall Occurs When There Is No Air Resistance An
object is in free fall only if gravity is pulling it down and no
other forces are acting on it.
End of Slide
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Section 1
Effects of Air Resistance on Falling Objects
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Section 1
Gravity and Motion
Orbiting Objects Are in Free Fall
• Two Motions Combine to Cause Orbiting An object is
orbiting when it is traveling around another object in
space.When a spacecraft orbits Earth, it is moving forward.
But the spacecraft is also in free fall toward Earth.
• Orbiting and Centripetal Force The unbalanced force
that causes objects to move in a circular path is called a
centripetal force. Gravity provides the centripetal force that
keeps objects in orbit.
End of Slide
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Section 1
How an Orbit Is Formed
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Section 1
Gravity and Motion
Projectile Motion and Gravity
• Horizontal Motion When you throw a ball,your hand
exerts a force on the ball that makes the ball move forward.
This force gives the ball its horizontal motion,which is
motion parallel to the ground.
• Vertical Motion A ball in your hand is prevented from
falling by your hand. After you throw the ball,gravity pulls it
downward and gives the ball vertical motion.
End of Slide
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 2
Newton’s Laws of Motion
Bellringer
Respond to the following question in your science journal:
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.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 2
Newton’s Laws of Motion
Objectives
• Describe Newton ’s first law of motion,and explain how it
relates to objects at rest and objects in motion.
• State Newton ’s second law of motion, and explain the
relationship between force, mass, and acceleration.
• State Newton ’s third law of motion, and give examples of
force pairs.
End of Slide
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 2
Newton’s Laws of Motion
Newton’s First Law of Motion
• 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
forever with the same velocity unless an unbalanced force
acts on them.
• Friction and Newton’s First Law Friction is an example
of an unbalanced force that stops motion.
End of Slide
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 2
Newton’s Laws of Motion
Newton’s First Law of Motion continued
• Inertia and Newton’s First Law Newton’s first law of
motion is sometimes called the law of inertia. Inertia is the
tendency of all objects to resist any change in motion.
• 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.
End of Slide
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 2
Newton’s Laws of Motion
Newton’s Second 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 The
acceleration of an object is always in the same direction as
the force applied.The cart shown on the next slide moved
forward because the push was in the forward direction.
• Expressing Newton’s Second Law Mathematically
Acceleration equals force divided by mass. F = ma
End of Slide
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Section 2
Mass, Force, and Acceleration
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Section 2
Newton’s Laws of Motion
Newton’s Third Law of Motion
• 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 action and reaction forces. However, action and
reaction forces in a pair do not act on the same object.
• All Forces Act in Pairs—Action and Reaction Newton’s
third law says that all forces act in pairs.
• The Effect of a Reaction Can Be Difficult to See The
force of gravity pulling the Earth toward objects is an
example.
End of Slide
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Section 3
Momentum
Bellringer
This section is about momentum. Make a list of five things
that have momentum and a list of five things that don’t have
momentum. What must you do to give an object
momentum? What about removing momentum? What
would happen to a hollow ball filled with water rolling
across a table if you stopped it then moved your hand away
quickly?
Explain your answers in your science journal.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section 3
Momentum
Objectives
• Calculate the momentum of moving objects.
• Explain the law of conservation of momentum.
End of Slide
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Section 3
Momentum
Momentum, Mass and Velocity
• What Is Momentum? The momentum of an object
depends on the object ’s mass and velocity.
• Calculating Momentum Momentum equals mass times
velocity.
End of Slide
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Section 3
Momentum
The Law of Conservation of Momentum
• Objects Sticking Together The mass of the combined
objects is equal to the masses of the two objects added
together. But, the combined objects move more slowly than
either object did before the collision.
• Objects Bouncing Off Each Other When 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.
• Conservation of Momentum and Newton’s Third Law
Conservation of momentum can be explained by Newton’s
third law of motion.
End of Slide
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Chapter 6
Forces and Motion
Concept Map
Use the following terms to complete the concept map on
the next slide: force, freefall, terminal velocity, gravity, air
resistance, projectile motion.
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Chapter 6
Concept Map
A
B
C
E
F
Force
Gravity
Free Fall
Terminal Velocity
Projectile Motion
Air Resistance
D
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Chapter 6
Concept Map
Copyright © by Holt, Rinehart and Winston. All rights reserved.