Experiment P10: Acceleration of a Dynamics Cart II (Motion Sensor)

Transcription

1 PASCO scientific Physics Lab Manual: P10-1 Experiment P10: (Motion Sensor) Concept Time SW Interface Macintosh file Windows file Newton s Laws 30 m 500 or 700 P10 Cart Acceleration II P10_CAR2.SWS EQUIPMENT NEEDED Interface dynamics cart motion sensor protractor adjustable feet, track track, 1.2 meter PURPOSE In this laboratory activity you will investigate the acceleration of a cart as it moves up and down an inclined plane. You will determine whether the acceleration of the cart is constant. THEORY If a cart moves on a plane that is inclined at an angle θ, the component of force acting on the cart in a direction that is parallel to the surface of the plane is mg sin θ, where m is the mass of the cart, and g is the acceleration due to gravity. mg sin θ θ mg The acceleration of the cart should be g sin θ, both up and down the inclined plane. PROCEDURE a = g sinθ For this activity, a motion sensor will measure the motion of a cart that is pushed up an inclined plane. The program calculates the velocity and acceleration of the cart as it moves up and down the inclined plane. PART I: Computer Setup 1. Connect the interface to the computer, turn on the interface, and then turn on the computer. 2. Connect the stereo phone plugs of the motion sensor to Digital Channels 1 and 2 on the interface. Plug the yellow-banded (pulse) plug into Digital Channel 1 and the second plug (echo) into Digital Channel 2. dg 1996, PASCO scientific P10-1

2 P10-2: Physics Lab Manual PASCO scientific 3. Open the file titled as shown; Macintosh P10 Cart Acceleration II Windows P10_CAR2.SWS The document will open with a Graph display. The Graph has plots of Position (m), Velocity (m/sec), and Acceleration (m/sec/sec) versus Time (sec). Note: For quick reference, see the Experiment Notes window. To bring a display to the top, click on its window or select the name of the display from the list at the end of the Display menu. Change the Experiment Setup window by clicking on the Zoom box or the Restore or Maximize button in the upper right hand corner of that window. PART II: Sensor Calibration and Equipment Setup You do not need to calibrate the motion sensor. 1. Place the track on a horizontal surface. Use the adjustable feet at one end of the track to raise that end. 2. Use the protractor to measure the angle of the inclined track. Record the angle in the Data Table. 3 Position the motion sensor at the high end of the track. The cart will start at the low end of the track and be pushed up toward the motion sensor. Motion Sensor Dynamics cart Track P , PASCO scientific dg

3 PASCO scientific Physics Lab Manual: P10-3 Preparing to Record Data Before recording any data for later analysis, experiment with the motion sensor to make sure it is aligned and can see the cart as it moves. Place the cart on the low end of the track (i.e., the end opposite to the motion sensor). Click the REC button ( ) to begin recording data. Give the cart a firm push up the track so the cart will move up the inclined plane toward and then away from the motion sensor. BE CAREFUL! Don t push the cart so firmly that it gets closer than 40 cm to the sensor. Click the STOP button ( bottom of the track. ) to end recording your sample data when the cart returns to the Click the Autoscale button ( ) to automatically rescale the Graph. If the plot of data is not smooth, check the alignment of the motion sensor. Erase your sample run of data. Select Run #1 in the Data list in the Experiment Setup window and press the Delete key. PART III: Data Recording 1. Prepare to measure the motion of the cart as it moves toward the motion sensor and then comes back down the track. Place the cart at the low end of the track. 2. Click the REC button ( ) to begin recording data. Give the cart a firm push toward the motion sensor. Continue collecting data until the cart has returned to the bottom of the track. 3. Click the STOP button ( ) to end data recording. Run #1 will appear in the Data list. (If the data points do not appear on the graph, check the alignment of the motion sensor and try again.) ANALYZING THE DATA Find the slope of the line of best fit in the plot of velocity versus time. The slope is the average acceleration of the cart. dg 1996, PASCO scientific P10-3

4 P10-4: Physics Lab Manual PASCO scientific 1. Click the Statistics button ( ) in the lower left corner of the Graph display to open the Statistics area in the right part of the Graph for all three plots. 2. Click the Autoscale button ( ) to rescale the graph to fit the data. 3. In the plot of velocity, use the cursor to click-anddraw a rectangle around the region of the plot that shows the cart s motion after the push and before it stopped at the bottom of the track. 4. Click the Statistics Menu button ( ) in the Statistics area of the velocity plot. Select Curve Fit, Linear Fit from the Statistics menu. 5. The slope of the best fit line (coefficient a2 in the Statistics area) is the average acceleration. Record the value in the Data Table. 6. In the plot of acceleration, use the mouse to click-and-draw a rectangle around the region of the plot that corresponds to the cart s motion after the push and before it stopped at the bottom of the track. 7. Click the Statistics Menu button in the Statistics area for the plot of acceleration. Select Mean from the Statistics menu. The Statistics area of the acceleration plot shows the mean value of the acceleration for your selected region. 8. Record the mean of the acceleration. P , PASCO scientific dg

5 PASCO scientific Physics Lab Manual: P Calculate the theoretical value for the acceleration of the cart and record it in the Data section. a = g sinθ DATA TABLE Item angle of track Value degrees acceleration (slope) m/sec 2 acceleration (mean) m/sec 2 acceleration (theoretical) m/sec 2 QUESTIONS 1. Describe the position versus time plot of the Graph display. Why does the distance begin at a maximum and decrease as the cart moves up the inclined plane? 2. Describe the velocity versus time plot of the Graph display. 3. Describe the acceleration versus time plot of the Graph display. 4. How does the acceleration determined in the plot of velocity compare to the mean value of acceleration from the plot of acceleration? 5. What is the percent difference between the acceleration determined in the plot of velocity and the theoretical value for acceleration? Remember, percent difference = theoretical actual theoretical 100% dg 1996, PASCO scientific P10-5