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Directed Reading A Section: Measuring Motion 1. Name something in motion that you cannot see moving.
OBSERVING MOTION BY USING A REFERENCE POINT ______ 2. An object in motion is moving in relation to an object that appears to a. stay in place. c. maintain constant velocity. b. keep moving. d. maintain constant acceleration. ______ 3. When an object changes position over time relative to a reference point, the object is a. speeding. c. decelerating. b. accelerating. d. moving. 4. For determining motion, the surface of Earth is a
common
.
5. Why are buildings, trees, and mountains all useful reference points?
6. Can a moving object be used as a reference point? Explain.
SPEED DEPENDS ON DISTANCE AND TIME 7. The speed of an object depends on the distance traveled and the
taken to travel that distance. 8. The SI unit for speed is
.
9. Why is it useful to calculate average speed?
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Directed Reading A continued 10. Explain how to calculate average speed.
11. When a person drives for several hours, how does the distance traveled in one hour usually compare with the distance traveled in other hours? Explain.
12. Suppose that, on a graph showing speed, there are two lines. One line represents speed per hour, and the other line represents average speed. Will both lines be exactly alike and in the same place on the graph? Explain.
VELOCITY: DIRECTION MATTERS ______13. Which of the following does NOT experience a change in velocity? a. A motorcyclist driving down a straight street applies the brakes. b. While maintaining the same speed and direction, an experimental car switches from gasoline to electric power. c. A baseball player running from first base to second base at 10 m/s comes to a stop in 1.5 seconds. d. A bus traveling at a constant speed turns a corner. 14. Why don’t birds end up at the same destination if they are flying exactly the same speed at all times?
15. What is the difference between velocity and speed?
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Directed Reading A continued 16. To find the resultant velocity, add velocities that are in the
direction(s). Subtract velocities that are in the
direction(s).
ACCELERATION 17. If your speed is not changing but your direction is changing, are you accelerating? Explain your answer.
18. Another name for acceleration in which velocity increases is
acceleration. 19. Negative acceleration is also called
.
20. Write the mathematical formula for calculating average acceleration.
21. A speedometer shows that a cyclist is going 1 m/s the 1st second, 2 m/s the 2nd second, and 3 m/s the 3r d second, as the cyclist continues straight south. How do you know the cyclist is accelerating?
22. How can you recognize acceleration on a graph?
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Directed Reading A continued 23. A graph shows a roller coaster increasing in velocity for the first eight seconds as it goes down the hill. Will the graph have an upward slope representing a roller coaster traveling down the hill? Explain your answer.
24. As long as something travels in a circle, is it always accelerating? Explain your answer.
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Answer Key Directed Reading A SECTION: MEASURING MOTION 1. Answers will vary. Sample answer: I
2. 3. 4. 5. 6.
7. 8. 9.
10.
11. 12.
13. 14. 15. 16. 17.
18. 19. 20.
21.
cannot see Earth moving. Yet, I know it moves (revolves) around the sun. A D reference point They make useful reference points because they do not move. Answers will vary. Sample answer: Yes; a moving object can be used as a reference point because it can be observed in relation to another moving object. time m/s, or meters per second Answers will vary. Sample answer: Objects don’t often travel at a constant speed. Average speed is the total distance traveled divided by the total time taken to travel that distance. The distances vary, because the speed is not constant. The line representing actual speed per hour will usually not be straight, because speed usually changes. The line representing average speed over the entire time will be straight, as it represents average speed as if it were the same speed all the time. B They are travelling in different directions. Velocity includes direction; speed does not include direction. same, opposite Yes, a change in direction is acceleration, just as a change in speed is acceleration. positive deceleration average acceleration = (final velocity – beginning velocity)/time for velocity change A change in velocity means acceleration. The cyclist’s velocity increased
from 1 m/s south to 3 m/s south. So, the cyclist is accelerating. 22. The graph shows velocity changing as time passes. 23. Answers will vary. Sample answer: The graph’s upward (positive) slope represents increasing velocity, which is what the roller coaster has as it travels downward. 24. Yes, it is always accelerating while it remains in a circle, because it is always changing direction.
SECTION: WHAT IS A FORCE? 1. 2. 3. 4. 5.
6.
7. 8. 9. 10. 11. 12.
13.
14. 15. 16. 17.
18.
force force newton object Answers will vary. Sample answer: I exert a force on a book when I open it; I exert a force on the keys of a keyboard when I type; and I exert a force on a chair when I sit on it. Answers will vary. Sample answer: An SUV sits in the parking lot; a computer sits on a desk; a desk sits on the floor. force force force force net force When both students apply force in the same direction, their forces are added together to produce a net force. The dog on the left will win the tug-ofwar, because the net force will be 1 N to the left. It will help you determine the effect of the force on the motion of an object. zero zero You need an unbalanced force. An unbalanced force causes motion in the direction of the greatest force. Yes. Answers will vary. Sample answer: A soccer ball that has been kicked continues to roll on the ground long after the ball is kicked.
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