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Chapter Introduction
Lesson 1 Describing Motion
Lesson 2 Position and Motion
Lesson 3 Acceleration
Chapter Wrap-Up
What do you think?
Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements.
1. Displacement is the distance an object moves along a path.
2. The description of an object’s position depends on the reference point.
3. Constant speed is the same thing as average speed.
Do you agree or disagree?
4. Velocity is another name for speed.
5. You can calculate acceleration by dividing the change in velocity by the change in distance.
6. An object accelerates when either its speed or its direction changes.
Do you agree or disagree?
• How does the description of an object’s position depend on a reference point?
• How can you describe the position of an object in two dimensions?
• What is the difference between distance and displacement?
Position and Motion
• reference point
• position
• motion
• displacement
Position and Motion
A description of a location usually states the location relative to a certain point.
Describing Position
relative
Science Use compared (to)
Common Use a member of your family
• A reference point is a starting point that can be used to locate a place or thing.
• A position is an object’s distance in a certain direction from a reference point.
Describing Position (cont.)
A complete description of your position includes a distance, a direction, and a reference point.
Describing Position (cont.)
Describing Position (cont.)
How does the description of an object’s position depend on a reference point?
An object’s position is described by a reference direction, such as toward the slide.
Describing Position (cont.)
The reference direction is the positive (+) direction and the opposite direction is the negative (-) direction.
Describing Position (cont.)
• When you describe a position using two directions, you are using two dimensions.
• To find a position in two dimensions you must choose a reference point, specify reference directions, and then determine the distance along each reference direction.
Describing Position in Two Dimensions
Describing Position in Two Dimensions (cont.)
How can you describe the position of an object in two dimensions?
Motion is the process of changing position.
Describing Changes in Position
motion
from Latin motere, means “to move”
The man in the boat is not in motion compared to his fishing pole. He is in motion compared to the buoy.
• Displacement is the difference between the initial (first) position and the final position of an object.
• Distance depends on the path taken.
• Displacement depends only on the initial and final positions.
Describing Changes in Position (cont.)
Distance and displacement are equal only if the motion is in one direction.
Describing Changes in Position (cont.)
What is the difference between distance and displacement?
• A reference point, a reference direction, and distance are needed to describe the position of an object.
• An object is in motion if its position changes relative to a reference point.
• The distance an object moves and the object’s displacement are not always the same.
A. one
B. two
C. three
D. none of the above
When you describe a position using two directions, how many dimensions are you using?
A. motion
B. reference point
C. displacement
D. direction
Which of these refers to the difference between the initial position and the final position of an object?
A. the positive direction
B. the negative direction
C. both of these
D. none of these
When describing an object’s position, the reference direction is which of these?
1. Displacement is the distance an object moves along a path.
2. The description of an object’s position depends on the reference point.
Do you agree or disagree?
• What is speed?
• How can you use a distance-time graph to calculate average speed?
• What are ways velocity can change?
Speed and Velocity
• speed
• constant speed
• instantaneous speed
• average speed
• velocity
Speed and Velocity
Speed is a measure of the distance an object travels in a unit of time.
What is speed?
What is speed?
You can calculate speed by dividing the distance traveled by the time it takes to go that distance.
What is speed? (cont.)
Constant speed is the rate of change of position in which the same distance is traveled each second.
What is speed? (cont.)
When the car’s speed changes, it moves a different distance each period of time.
What is speed? (cont.)
• Instantaneous speed is speed at a specific instant in time.
• Average speed is the total distance traveled divided by the total time taken to travel that distance.
What is speed? (cont.)
• Graphs that show comparisons between distance and time are called distance-time graphs.
• Constant speed is shown as a straight line on a distance-time graph.
Distance-Time Graphs
• You can use distance-time graphs to compare the motion of two different objects.
• The steeper line indicates a faster speed.
Distance-Time Graphs (cont.)
You can use distance-time graphs to calculate the average speed of an object.
Distance-Time Graphs (cont.)
How can you use a distance-time graph to calculate average speed?
Distance-Time Graphs (cont.)
If the speed of an object changes instead of being constant, its motion on a distance-time graph is a curved line.
Velocity is the speed and the direction of a moving object.
Velocity
velocity
from Latin velocitas, means “swiftness, speed”
• The velocity of an object can be represented by an arrow.
• A greater speed is shown by a longer arrow.
• The arrow points in the direction of the object’s movement.
Velocity (cont.)
Velocity (cont.)
Velocity changes when the speed of an object changes, when the direction that the object moves changes, or when both the speed and the direction change.
• Speed is a measure of the distance an object travels in a unit of time. You can describe an object’s constant speed, instantaneous speed, or average speed.
• A distance-time graph shows the speed of an object.
A. speed
B. constant speed
C. instantaneous speed
D. average speed
The total distance traveled divided by the total time taken to travel that distance is known as which of these?
A. units of speed
B. constant speed
C. units of time
D. average speed
Units of speed are units of distance divided by which of these?
A. a wavy line
B. a crooked line
C. a straight line
D. a curved line
How is constant speed represented on a distance-time graph?
3. Constant speed is the same thing as average speed.
4. Velocity is another name for speed.
Do you agree or disagree?
• What are three ways an object can accelerate?
• What does a speed-time graph indicate about an object’s motion?
Acceleration
• Acceleration is a measure of how much the velocity of an object changes in a unit of time.
• An object accelerates when its velocity changes as a result of increasing speed, decreasing speed, or a change in direction.
Acceleration—Changes in Velocity
Acceleration has a direction and can be represented by an arrow.
Acceleration—Changes in Velocity (cont.)
Acceleration—Changes in Velocity (cont.)
What are three ways an object can accelerate?
Acceleration is a change in velocity during a time interval divided by the time interval during which the velocity changes.
Calculating Acceleration
Acceleration is in the direction of motion if it is positive and opposite the direction of motion if it is negative.
Calculating Acceleration (cont.)
• A speed-time graph shows how speed changes over time.
• A speed-time graph has time on the horizontal axis—the x-axis, and speed on the vertical axis—the y axis.
Speed-Time Graphs
Speed-Time Graphs (cont.)
horizontal
from Greek horizein, means “limit, divide, separate”
vertical
from Latin verticalis, means “overhead”
An object at rest is not moving, so its speed is always zero.
Speed-Time Graphs (cont.)
For an object moving at constant speed, the speed-time graph is a horizontal line.
Speed-Time Graphs (cont.)
The line on the speed-time graph for an object that is speeding up has an upward slope.
Speed-Time Graphs (cont.)
Speed-Time Graphs (cont.)
The line on the speed-time graph for an object that is slowing down has a downward slope.
Speed-Time Graphs (cont.)
What does a speed-time graph show about the motion of an object?
• There are several ways to describe motion.
• You can describe position by direction and distance from a reference point.
• You can compare distance and displacement to find average speed.
• You can describe velocity by speed and direction.
Summarizing Motion
• An object accelerates if it speeds up, slows down, or changes direction.
• Acceleration in a straight line can be calculated by dividing the change in speed by the change in time.
• A speed-time graph shows how an object’s speed changes over time.
A. increasing speed
B. decreasing speed
C. a change in direction
D. all of the above
An objects accelerates when its velocity changes as a result of which of these?
A. the horizontal axis (the x-axis)
B. the vertical axis (the y-axis)
C. both of these
D. neither of these
On a speed-time graph, where is time located?
Which of these refers to a change in velocity during a time interval divided by the time interval during which the velocity changes?
A. acceleration
B. speed
C. velocity
D. none of these
5. You can calculate acceleration by dividing the change in velocity by the change in distance.
6. An object accelerates when either its speed or its direction changes.
Do you agree or disagree?
Key Concept Summary
Interactive Concept Map
Chapter Review
Standardized Test Practice
The motion of an object can be described by the object’s position, velocity, and acceleration.
• An object’s position is its distance in a certain direction from a reference point.
• The position of an object in two dimensions can be described by choosing a reference point and two reference directions, and then stating the distance along each reference direction.
• The distance an object moves is the actual length of its path. Its displacement is the difference its initial position and its final position.
Lesson 1: Position and Motion
Lesson 2: Speed and Velocity
• Speed is the distance an object moves in a unit of time.
• An object moving the same distance each second is moving at a constant speed. The speed of an object at a certain moment is its instantaneous speed.
• You can calculate an object’s average speed from a distance-time graph by dividing the distance the object travels by the total time it takes to travel that distance.
• Velocity changes when speed, direction, or both speed and direction change.
• Acceleration is a change in velocity over time. An object accelerates when it speeds up, slows down, or changes direction.
• A speed-time graph shows the relationship between speed and time and can be used to determine information about the acceleration of an object.
Lesson 3: Acceleration
A. displacement
B. position
C. reference direction
D. reference point
What term refers to a starting point that can be used to locate a place or thing?
A. three
B. one
C. two
D. none of these
Distance and displacement are equal only if the motion is in how many directions?
A. comparisons between the motion of two objects
B. the average speed of an object
C. comparisons between distance and time
D. all of the above
Which of the below can be illustrated with a distance-time graph?
A. It is positive.
B. It is negative.
C. The object is at rest.
D. The speed-time graph has a downward slope.
If acceleration is in the direction of motion, which of these is true?
A. the horizontal axis (the x-axis)
B. the vertical axis (the y-axis)
C. Speed is not indicated on a speed-time graph.
D. The speed is the slope of the line.
Where is speed located on a speed-time graph?
A. the positive direction
B. the negative direction
C. the reference direction
D. none of these
When you describe an object’s position, the opposite direction is which of these?
A. displacement
B. reference point
C. motion
D. velocity
Which term refers to the process of changing position?
A. velocity
B. constant speed
C. average speed
D. instantaneous speed
Which of these describes the speed and the direction of a moving object?
A. the speed of an object changes
B. the direction an object moves changes
C. both the speed and direction of an object changes
D. all of the above
Which of these results in a change of velocity?
A. direction
B. speed
C. acceleration
D. velocity
Which term refers to a measure of how much the velocity of an object changes in a unit of time?
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