Experiment P12: Pushing and Pulling a Dynamics Cart (Force Sensor, Motion Sensor)

Transcription

1 PASCO scientific Physics Lab Manual: P12-1 Experiment P12: Pushing and Pulling a Dynamics Cart (Force Sensor, Motion Sensor) Concept Time SW Interface Macintosh file Windows file Newton s Laws 30 m 500 or 700 P12 Push-Pull a Cart P12_PUSH.SWS EQUIPMENT NEEDED Interface dynamics cart motion sensor force sensor bracket & bumpers ±50 Newton force sensor screwdriver, Phillips head, #0 adjustable feet, track (two) track, 1.2 meter or 2.2 meter balance (to measure mass) PURPOSE The purpose of this laboratory activity is to investigate the relationship of the force exerted on a cart, the mass of the cart, and the acceleration of the cart as it moves. THEORY Isaac Newton described the relationship of acceleration to net force and mass of an object as follows: The acceleration of an object is directly proportional and in the same direction as the net force on the object, but inversely proportional to the mass of the object. PROCEDURE a = Fnet m For this activity, you will push and pull a dynamics cart back-and-forth on a level track. The motion sensor measures the motion of a cart, and the force sensor measures the force you exert on the cart. The program calculates the acceleration of the cart as it moves. The graph of force versus acceleration reveals the mass of the moving object. PART I: Computer Setup 1. Connect the interface to the computer, turn on the interface and then turn on the computer. 2. Connect the motion sensor s stereo phone plugs 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 Connect the force sensor s DIN plug to Analog Channel A on the interface. dg 1996, PASCO scientific P12-1

2 P12-2: Physics Lab Manual PASCO scientific 4. Open the file titled as shown; Macintosh P12 Push-Pull a Cart Windows P12_PUSH.SWS The document will open with a Graph display of Force (Newtons) versus Acceleration (m/s/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. 5. The Sampling Options are: Periodic Samples = Fast at 500 Hz, Digital Timing = Hz. 6. The setup for the Force Sensor has been changed so that a push to the left is negative and a pull to the right is positive. PART II: Sensor Calibration and Equipment Setup You do not need to calibrate the motion sensor or the force sensor for this activity. (If you wish to calibrate the sensors, refer to the instruction manuals for the sensors.) P , PASCO scientific dg

3 PASCO scientific Physics Lab Manual: P Place the track on a horizontal surface. Level the track by placing a cart on the track. If the cart rolls one way or the other, use the adjustable feet at one end of the track to raise or lower that end until the track is level and the cart will not roll one way or the other. 2 Position the motion sensor at the left end of the track. The cart will be pushed back and forth in front of the motion sensor. The minimum distance from the sensor to the target is 0.40 m (40 cm). Put a mark on the track 40 cm from the motion sensor. 3. Use a #0 Phillips head screwdriver to mount the force sensor onto the accessory tray of the cart so the hook end of the force sensor points away from the motion sensor. Minimum distance = 40 cm Force Sensor Motion Sensor Dynamics cart 4. Measure and record the mass of the cart plus force sensor in the Data Table. 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 one end of the track. Press the tare button on the side of the force sensor to zero the force sensor. Click the REC button ( ) in the Experiment Setup window to begin recording data. Firmly grasp the hook of the force sensor and pull and push the force sensor to make the cart move back and forth. Make sure the cart does not come too close to the motion sensor. Click the STOP button ( ) to end recording your sample data. In the Graph display, click the Autoscale button ( ) to automatically rescale the graph. If the plot of data is very chaotic, check the alignment of the motion sensor. Erase your sample data. Select Run #1 in the Data list in the Experiment Setup window and press the Delete key. dg 1996, PASCO scientific P12-3

4 P12-4: Physics Lab Manual PASCO scientific PART III: Data Recording 1. Press the tare button on the side of the force sensor to zero the force sensor. 2. Click the REC button ( ) to begin recording data. At the same time begin pulling and pushing on the hook of the force sensor to make the cart move back and forth. 3. Push and pull the cart back and forth four or five times. 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 force versus acceleration curve for the cart as it moves back and forth in front of the motion sensor. The slope is the mass of the cart plus force sensor. 1. Click the Autoscale button ( ) to rescale the Graph to fit the data. 2. Click the Statistics button ( ) to open the Statistics area at the right side of the Graph. 3. Click the Statistics Menu button ( ). Select Curve Fit, Linear Fit from the Statistics menu. 4. The slope of the line of best fit (coefficient a2) is the mass of the cart plus force sensor. Record the mass of the cart plus force sensor. DATA TABLE Item Value mass of cart & sensor (measured) mass of cart & sensor (slope) kg kg P , PASCO scientific dg

5 PASCO scientific Physics Lab Manual: P12-5 QUESTIONS 1. Why should the slope of the force versus acceleration plot equal the object s mass? 2. What is the percentage difference between the actual and experimental mass? Remember, percent difference = theoretical actual theoretical 100% dg 1996, PASCO scientific P12-5