LAB 1: INTRODUCTION TO MOTION

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Lab 1: Uniform Motion INVESTIGATION 1: POSITION-TIME GRAPHS Activity 1-1: Producing Position-Time Graphs as You Move The purpose of this activity is to learn how to relate graphs of position versus time to the motions they represent. You will need Pasco’s Data Studio software, CI-750 Interface and a Motion detector. You will also need a two-meter stick or tape on floor placed at one meter intervals. Representing location: The meter stick is a portion of a coordinate system that extends in both directions. The range-finder is at the origin of this coordinate system, with its speaker aimed along the positive x –axis. At any instant in time objects can occupy various locations on that axis. Unless otherwise stated, the units on all axes will be in meters. Motion detector -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 In the diagram above, the professor has position x = +2 m, and the wolf has x = – 5 m. The range-finder is at the “origin” x = 0 m, so all locations are measured from (relative to) it. An object’s location is represented by an arrow from the origin to the object : tail at origin, tip at object. Because the orientation of the arrow matters, this is called the position “vector”. On the diagram above, draw the location vector for the wolf, and also draw the position vector for the prof. Note that the range-finder cannot detect echoes from objects behind it (unlike the professor), so you will not encounter negative positions in this lab’s data. You may encounter them in homework questions however. As you walk or run along the x–axis, your distance from the range-finder is determined (by timing the reflected “click”), and the graph on the computer screen will display your position at each instant in time, measured from the origin. Procedure: 1. Log in to the computer. Open the 202Labs folder with a DOUBLE CLICK on the folder icon; then open the Lab 1 folder. Load Activity 1-1 into the DataStudio application by dragging the Activity icon onto the DataStudio icon. 2. Begin graphing positions by clicking the green [START] button at the top left. Verify that the range-finder measures positions correctly, by standing still at a measured distance from it. Describe the shape of the position-time graph you obtain: ____________________________. Make sure the detector is measuring correctly before you continue. The sonic ranger gives the position of the nearest object that makes an echo, so it will give the position of anyone who crosses the straight-line path between you and the detector. If you are not in the path of the (focused) sound wave, it might detect the distant wall. Try standing at x = 2 m, but swinging your arms as if walking. It will not correctly measure objects closer than ½ meter, so don’t make graphs at close distances. 3. Now move away and towards the motion detector at different speeds until you understand the different shapes of the position-time graphs. Discuss your understanding with your lab partners until you all agree. How is a slow speed indicated on the location-time graph? Fast Page 1- 2
Position (m) Position (m) Position (m) Position (m) Lab 1: Uniform Motion speed? What does the graph look like when you move toward the detector? Away from it? Note it is better to use the terms away and towards, rather than forward and backward, since the latter might be confused with the walker’s orientation as they move. After completing this activity you should be able to look at a distance-time graph and describe the motion of an object. You should also be able to look at the motion of an object and sketch a graph representing that motion. The next step is to give you some practice in doing this. 4. On the axes below, predict the shape of the position-time graphs for each of the described motions with a broken line. Then check your predictions by moving in the described way and draw the actual curve with a solid line. a. Use broken line first predict a distancetime graph, walking away from the detector (origin) slowly and steadily. Now check your prediction and draw it with a solid line. b. Use broken line first predict a distancetime graph, walking away from the detector (origin) medium fast and steadily. Now check your prediction and draw it with a solid line. Time (s) c. Use broken line first predict a distancetime graph, walking toward the detector (origin) slowly and steadily. Now check your prediction and draw it with a solid line. Time (s) d. Use broken line first predict a distancetime graph, walking away from the detector (origin) starting off medium fast and slowing down to a stop. Now check your prediction and draw it with a solid line. Time (s) Time (s) Question 1-1: What is the difference between the graph made by walking away from the detector slowly and steadily and the one made walking away quickly and steadily? Question 1-2: What is the difference between the graph made by walking steadily toward the motion detector and one made walking steadily away from the motion detector? Page 1- 3
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LAB 1: INTRODUCTION TO MOTION

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