# 2 Motion 3 Acceleration MAIN R

```2 Motion
3 Acceleration
4(A)
MAINIDEA
Write the Main Idea for this lesson.
REVIEW VOCABULARY
Recall the definition of the Review Vocabulary term.
velocity
velocity
NEW VOCABULARY
Use your book to define the terms below.
acceleration
acceleration
centripetal acceleration
centripetal acceleration
Use a dictionary to define constant to its scientific meaning.
constant
constant
Science Notebook • Motion
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Analyze why we say an object is accelerating, when we usually mean
that it is speeding up. An object that is slowing down also is
accelerating.
3 Acceleration (continued)
Student Edition, pp. 56–58
Analyze Label each of the four parts of the graph with either a plus sign,
a minus sign, or a zero to indicate where the car’s acceleration is positive,
negative, or zero.
Velocity and Acceleration
Speed
Speed Changing Over Time
1 2 3 4 5 6 7 8 9
10min
Time
• Describe the relationship between speed and acceleration as shown in
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GET IT?
Motion in Two
Dimensions
Identify three ways that an object can accelerate.
Compare the results of applying the acceleration equation in the
following two cases: (1) an object that goes from 0 to 10 m/s in 4 s, and
(2) then goes from 10 m/s to 30 m/s in 8 s.
(1) a = (vf – vi)/t
=
=
(2) a = (vf – vi )/t
=
Science Notebook • Motion
27
=
3 Acceleration (continued)
Student Edition, pp. 58–59
Analyze why the SI unit of acceleration is m/s2.
Circular Motion
Create a top view of an object moving in a circle at constant speed, such
as a ball on a string. Show at least two positions of the object. At each
position, draw an arrow for the object’s velocity and another arrow for the
centripetal acceleration of the object.
Define the term centripetal acceleration.
Science Notebook • Motion
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GET IT?
3 Acceleration (continued)
Student Edition, pp. 59–60
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Projectile Motion
Model a ball thrown horizontally. Sketch the path of the ball and draw
arrows showing its horizontal and vertical velocity at three points along
the path. Vary the length of your arrows to show the magnitude of the
velocities.
SYNTHESIZE IT
Distinguish between average acceleration and instantaneous acceleration. Be sure to explain how
the acceleration equation calculates average acceleration, instantaneous acceleration, or both.
Science Notebook • Motion
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3 Acceleration (continued)
REVIEW IT !
25. MAINIDEA Describe the acceleration of your bicycle as you ride it from your home
to the store.
26. Determine the change in velocity of a car that starts at rest and has a final velocity of
20 m/s north.
27. Describe the motion of an object that has an acceleration of 0 m/s2.
28. Think Critically Suppose a car traveling in a straight line is accelerating so that its
speed is increasing. First, describe the line that you would plot on a speed-time graph
for the motion of the car. Then describe the line that you would plot on a distance-time
graph.
30. Calculate Speed A sprinter leaves the starting blocks with an acceleration of 4.5 m/s2.
What is the sprinter’s speed 2 s later?
Science Notebook • Motion
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29. Calculate Time A ball is dropped from a cliff and has an acceleration of 9.8 m/s2. How
long will it take the ball to reach a speed of 24.5 m/s?
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