1. Chapter 5: Investigating Motion
UNIT 3
Chapter 5: Investigating Motion
Chapter 5: Investigating Motion
Finding a store in a shopping mall and driving to a friend’s house are tasks that you might do without any thought. You might not think about motion when you do tasks like these, but these tasks involve motion and the description of motion.
Sample answers: nouns could include left, right, speed, velocity, acceleration, direction, position; adjectives could include fast, slow, straight ahead,
List some words that describe motion.
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2. 5.1 Describing Motion UNIT 3
Chapter 5: Investigating Motion
Section 5.1
5.1 Describing Motion
Telling someone how to get from one place to another, such as from their home to the movie theatre, is an example of describing motion.
How would you describe the location of the woman holding the purse on the left side of the photograph relative to the man in the bowtie behind the counter?
Sample answers: she is in front of him; he is behind her; she is to his right; he is to her right; they are approximately 2 m apart.
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3. UNIT 3
Chapter 5: Investigating Motion
Section 5.1
Position
When you describe the position of an object, you must include a distance, a direction, and a reference point.
Distance is a unit of length, and the SI base unit for distance is the metre.
Compass points, or a “+” and “−” if you are using a number line, are used to describe direction.
Number lines and coordinate systems are often used to specify position.
What are two ways that you could describe the position of the skater on the right?
+9 m or 9 m east of the fire hydrant
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4. Position UNIT 3 Motion is the process of changing position.
Chapter 5: Investigating Motion
Section 5.1
Position
Motion is the process of changing position.
Two ways of describing motion are distance and displacement.
Displacement is the straight-line distance, or the difference, between the initial position and the final position of an object.
What distance did the player run in A, B, and C, and what is the displacement for each?
The distance equals 27.4 m, and the displacement equals 27.4 m.
The distance equals 54.8 m, and the displacement equals 38.7 m.
The distance equals m, and the displacement equals 0.
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5. Scalar Quantities and Vector Quantities
UNIT 3
Chapter 5: Investigating Motion
Section 5.1
Scalar Quantities and Vector Quantities
A scalar is a quantity that has only magnitude (size) and is represented by a number and units. Scalars are distance, time, and temperature.
A vector is a quantity that has both magnitude (size) and direction. Displacement and position are both vectors.
Arrows are often used to represent vectors. The length of the arrow represents the size of motion. The arrow point represents the direction of motion.
What is the runner’s displacement in the figure below?
40 m[E]—this is a vector quantity
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6. Calculating Displacement
UNIT 3
Chapter 5: Investigating Motion
Section 5.1
Calculating Displacement
Displacement—the change in position—is represented by the equation below:
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7. Choosing a Reference Point
UNIT 3
Chapter 5: Investigating Motion
Section 5.1
Choosing a Reference Point
An object’s position may change relative to one reference point, but it may not be moving relative to another reference point.
When describing motion, it is important to include the reference point so your description will be clear.
Describe a reference point that could be used to indicate that the man in the boat is NOT moving, and describe another reference point that could be used to show that the man IS moving.
The boat itself could be used to show that the man is not moving, and the buoy could be used to show that the man is moving.
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8. Determining the Time Interval
UNIT 3
Chapter 5: Investigating Motion
Section 5.1
Determining the Time Interval
The time interval is the difference between when an event begins and when that event ends.
The SI unit for time is the second, s, and the symbol for time is t.
The equation for finding the time interval is
t = tf – ti
Use the equation above to find the time interval of your science class.
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9. UNIT 3
Chapter 5: Investigating Motion
Section 5.1
Uniform Motion
Uniform motion is motion in which the object’s displacement is equal for each time interval.
Uniform motion is rare because frictional forces usually act on the object.
Why does the motion diagram (B) show the uniform motion of the billiard balls more clearly than the photograph (A)?
Sample answer: The motion diagram has a number line that can be used to find reference points, and the photograph does not.
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10. Graphing Uniform Motion
UNIT 3
Chapter 5: Investigating Motion
Section 5.1
Graphing Uniform Motion
Position-time graphs show the position of an object over time.
When the motion of an object is a straight line on a position-time graph, the object has uniform motion.
The graph on the left side because the data points fall on a straight line.
Which graph represents an object that has uniform motion?
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11. Analyzing a Position-Time Graph
UNIT 3
Chapter 5: Investigating Motion
Section 5.1
Analyzing a Position-Time Graph
A positive slope on a position-time graph indicates that the object is moving in the positive direction.
A negative slope on a position-time graph indicates that the object is moving in the negative direction.
A zero slope on a position-time graph indicates that the object is not moving over time.
Is the motion of the object positive or negative in this position-time graph?
Is the motion uniform? How do you know?
Sample answer 1: The motion of the object is negative.
Sample answer 2: The object has uniform motion because a plot of the motion on a position-time graph is a straight line.
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12. UNIT 3
Chapter 5: Investigating Motion
Section 5.1
Section 5.1 Review
When you describe the position of an object, you must include a distance, direction, and reference point.
Units of length, such as metres and kilometres, are used to measure distance.
Compass points and coordinate systems are often used to describe positions.
Two ways of describing motion—a process of changing position—are distance and displacement.
A scalar is a quantity that has only magnitude, such as distance, time, and temperature.
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13. UNIT 3
Chapter 5: Investigating Motion
Section 5.1
Section 5.1 Review
A vector is a quantity that has both magnitude and direction, such as displacement and position.
Vectors are used to represent motion, and they are added to find resultant vectors.
Position-time graphs indicate if an object is moving in the positive direction, in the negative direction, or not moving at all.
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14. 5.2 Distance, Time, and Speed
UNIT 3
Chapter 5: Investigating Motion
Section 5.2
5.2 Distance, Time, and Speed
Speed, v, is the distance an object moves in a certain length of time.
Speed can be constant or changing. Constant speed is when an object travels the same distance for each time interval. Changing speed is when an object travels a different distance for each time interval.
If there were no labels on the figure, how could you tell which car had constant speed and which car had changing speed?
Sample answer: The car that had constant speed moves the same distance during each time interval.
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15. Distance, Time, and Speed
UNIT 3
Chapter 5: Investigating Motion
Section 5.2
Distance, Time, and Speed
The slope of the line between any two points on a distance-time graph is the average speed the object is moving during that time interval.
The average speed of an object is the distance travelled divided by the time it takes to travel that distance.
The equation to calculate average speed is
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16. Distance, Time, and Speed
UNIT 3
Chapter 5: Investigating Motion
Section 5.2
Distance, Time, and Speed
The slope of the line on a distance-time graph can be calculated using the following formula:
Choose two points on the graph and determine the slope of the line, which is the average speed of the object.
From page 222 of the student textbook:
slope = yf – yi = 36 m – 12 m = 8 m/s Therefore, the average speed between 4.5 s and 1.5 s was 8 m/s
xf – xi s – 1.5 s
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17. Distance, Time, and Speed
UNIT 3
Chapter 5: Investigating Motion
Section 5.2
Distance, Time, and Speed
Instantaneous speed is speed at a specific instant of time.
The speedometer in a car displays instantaneous speed.
What is the instantaneous speed shown on this car speedometer?
The instantaneous speed of the car is 100 km/h.
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18. UNIT 3
Chapter 5: Investigating Motion
Section 5.2
Section 5.2 Review
Speed is the distance an object moves in a certain length of time.
Speed is a scalar quantity.
There are many kinds of speed, including constant speed, changing speed, average speed, and instantaneous speed.
The slope of the line between any two points on a distance-time graph is the average speed the object is moving during that time interval.
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19. 5.3 Position, Displacement, and Velocity
UNIT 3
Chapter 5: Investigating Motion
Section 5.3
5.3 Position, Displacement, and Velocity
Velocity is a vector quantity that describes an object’s displacement during a specific time interval or an object’s rate of change of position.
An object can have constant velocity or changing velocity.
How do speed and velocity differ?
Constant velocity is when an object travels at the same speed and in the same direction for each time interval.
Changing velocity is when an object’s speed or direction, or both speed and direction change for each time interval.
Sample answer: Speed is a scalar, and it has only magnitude. Velocity is a vector, and it has both magnitude and direction.
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20. Position, Displacement, and Velocity
UNIT 3
Chapter 5: Investigating Motion
Section 5.3
Position, Displacement, and Velocity
The slope between any two points on a position-time graph gives the magnitude of the object’s average velocity during that time interval.
Average velocity, vave, is the displacement of an object divided by the time interval it takes to travel the displacement.
Instantaneous velocity is the velocity (both magnitude and direction) at a specific instant of time.
Calculate average velocity using the following equation:
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21. Position, Displacement, and Velocity
UNIT 3
Chapter 5: Investigating Motion
Section 5.3
Position, Displacement, and Velocity
What does the bear appear to be doing after 13.5 h?
Sample answer: The bear is not moving and appears to be resting.
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22. UNIT 3
Chapter 5: Investigating Motion
Section 5.3
Section 5.3 Review
Velocity is a vector quantity that describes an object’s displacement during a specific time interval or an object’s rate of change of position.
There are many kinds of velocity, including constant velocity, changing velocity, average velocity, and instantaneous velocity.
The slope between any two points on a position-time graph gives the magnitude of the object’s average velocity during that time interval.
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