Forces and Motion - Position and Motion PDF

LESSON 1 Force...

LESSON 1 Forces and Motion Position and Motion Key Concept How can you describe What do you think? Read the two statements below and decide the position and motion whether you agree or disagree with them. Place an A in the Before of a train outside the column if you agree with the statement or a D if you disagree. After window? you’ve read this lesson, reread the statements to see if you have changed your mind. Before Statement After Displacement is the distance an object moves along a path. The description of an object’s position depends on the reference point. Mark the Text Where are you right now? Create an Outline As you read, make an outline to How would you describe where you are right now? You might summarize the information say that you are sitting one meter to the left of your friend. You in the lesson. Use the main might explain that you are at home, which is two houses north headings in your outline. Use your outline to review of your school. the lesson. Describing Position What do these descriptions have in common? Each states your location relative to a certain point. This point is called the reference point. A reference point is the starting point you choose to describe the location, or position, of Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. an object. The reference point in the first example is your friend. In the second example, it is your school. Each description of your location also includes your distance and direction from Academic Vocabulary the reference point. Describing your location in this way defines specify your position. In the first example, the distance is one meter. (verb) to indicate or The direction is to the left, and the reference point is your identify friend. In the second example, the distance is two houses. The direction is north, and the reference point is your school. A position is an object’s distance in a certain direction from a reference point. A complete description of your position includes a distance, a direction, and a reference point. Reading Essentials Forces and Motion 1 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Scientific Vocabulary The Reference Direction Sometimes direction is described reference direction using the words positive or negative. The reference direction is (noun) a direction that the positive (+) direction. The opposite direction is the negative (-) you choose from a starting direction. Suppose east is the reference direction in the diagram point to describe an object’s position below. The museum’s entrance is 80 m east of a bus stop. The library is 40 m west of the bus stop. You could say that the museum is +80 m from the bus stop and the library is -40 m from the bus stop. Using the words positive or negative to describe direction can help explain changes in an object’s position. East Library Bus stop 20 m Museum Scientific Vocabulary Moving in Two Dimensions Sometimes you need to use more dimension than one reference direction to describe an object’s position. (noun) a measurement of When you describe position using two directions, you are using RE_P360_109A_NGMSS-BANK something, such as height two dimensions. or width Describing Position in Two Dimensions To describe a position on a map, you might choose north and east or south and west as the reference directions. Sometimes north, south, Academic Vocabulary east, and west are not the most useful reference directions. imagine Imagine that you are looking at a skyscraper. You might describe (verb) to form ideas in a certain window as “up” and “to the left.” your mind Suppose you want to locate your classmate’s home on a map. Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. To find a position in two dimensions, first choose a reference point. You could choose your home as a reference point. Next, give specific reference directions. For example, south and east. Then, determine the distance along each reference direction. For example, your classmate’s home might be one block south and four blocks east of your home. What is motion? Sometimes you need to describe how an object’s position changes. Suppose a boat is floating on a lake. Motion How do you know whether the boat has moved throughout the day? You know this when its position changes relative to, or compared to, something else. Motion is the process of changing position. 2 Forces and Motion Reading Essentials THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Observing Motion Is the man in the figure below in motion? Use the fishing pole as the reference point. The positions of the Scientific Vocabulary man and the pole do not change relative to each other. The man relative does not move relative to the pole. When the buoy is the (adjective) compared to reference point, the man’s distance from the buoy changes. The something or someone else man is in motion relative to the buoy. Motion Using Reference Points How would you describe the RE_P360_112A_NGMSS-BANK position of the soccer player in the figure? If the reference point is the goal, or point A, the player’s position is 10 m in front of the goal. If the reference point is center field, point B, the position is 40 m toward the goal. The actual location of the player does not change. The description of the position changed because the reference point changed. Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. C 10 m 41.2 m B A 40 m 10 m D Reading Essentials Forces and Motion 3 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Distance and Displacement Suppose a baseball player runs the bases. Distance is the length of the path the player runs. Suppose he runs 25 m to get to first base. When he gets to second base, he has run 25 m + 25 m = 50 m. Displacement is the difference between the initial (first) position and the final position of an object. The initial position is home plate. At first base, the player’s distance and displacement are the same. He has run a distance of 25 m and he is 25 m from home plate, where he started. At second base, distance and displacement are different. The player has run a distance of 50 m, but his displacement is 35 m from home plate. Once the player has runs all the bases and is back at home plate, he has run 100 m (25 m × 4), but his displacement is 0 m. His starting position and ending position are the same—home plate. Distance depends on the path taken. Only the starting and ending positions matter in displacement. Notice that distance and displacement are equal only if the motion is in one direction. What do you measure to determine motion? How fast do you walk when you are hungry and you smell good food in the kitchen? How fast do you move when you have a difficult chore to do? Sometimes you move quickly. Other times you might move slowly. Changes Over Time One way you can describe how fast you move is to determine your speed. Speed is the measure of the distance an object travels per unit of time. Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. 4 Forces and Motion Reading Essentials THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Constant and Changing Speed Speed is either constant or changing. Look at the figure at below. The stopwatches show the girl’s motion every second for 6 seconds. In the first 4 seconds, she travels the same distance during each second. This means that she was moving with constant, or unchanging, speed. When the girl starts running, the distance she travels each second gets larger and larger. The girl’s speed changes. Average Speed Suppose you want to know how fast you traveled from the park to the library. As you moved, your speed RE_P360_115A_NGMSS-BANK changed from second to second. Therefore, in order to describe your speed, you describe the average speed of the entire trip. Average speed is a ratio. It is the distance an object moves divided by the time it takes for the object to move that distance. If you traveled the 1-km distance to the library in 15 min, or 0.25 h, your average speed was 1 km/0.25 h, or 4 km/h. Speed and Direction When you describe your motion to a Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. friend, you might say how fast you are traveling. You are describing your speed. You could give your friend a better description of your motion if you also state the direction in which you are moving. Velocity is the speed and direction of an object’s motion. Velocity is a vector. A vector is a quantity that has magnitude and direction. Arrows often represent vectors. The length of the arrow represents the speed of an object. The arrow points in the direction in which the object is moving. Reading Essentials Forces and Motion 5 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Constant and Changing Velocity Velocity is constant, or does not change, when an object’s speed and direction of Scientific Vocabulary movement do not change. Look at arrows in the left box in the segment figure below. Each segment of the arrow shows the distance and (noun) a part of the direction the cyclists move in a given unit of time. Each something segment is the same length. This means the cyclists are moving the same distance and in the same direction during each unit of time. Both speed and direction of movement are constant, so the cyclists are moving at a constant velocity. The arrows in the middle box get larger each second. The speed is changing, so the velocity is also changing. Velocity can change even if the speed of an object remains constant. Recall that velocity includes an object’s speed and the direction it is traveling. Constant Velocity Changing Velocity Changing Speed Changing Direction 0s 1s 2s 3s 4s 0s 1s 2s 3s 4s How can a graph help you understand an object’s motion? RE_P360_121A_NGMSS-BANK In the study of motion, the two measurements that are compared are time and distance. Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. Distance-Time Graphs Graphs that show comparisons between time and distance are called distance-time graphs. The change in distance is the same each second on the graph below, which represents an object moving at constant speed. Constant speed is shown as a straight line on distance-time graphs. Distance-Time Graph 60 50 Distance (m) 40 30 20 10 0 1 2 3 4 5 6 Time (s) 6 Forces and Motion Reading Essentials THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED. RE_P360_111A_NGMSS-BANK  Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind? Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. Reading Essentials Forces and Motion 7 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.