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1、Experiment18Physics with Computers 18 - 1Work and EnergyNo springs Work is a measure of energy transfer. In the absence of friction, when positive work is done on an object, there will be an increase in its kinetic or potential energy. In order to do work on an object, it is necessary to apply a for
2、ce along or against the direction of the objects motion. If the force is constant and parallel to the objects path, work can be calculated usingWF swhere F is the constant force and s the displacement of the object. If the force is not constant, we can still calculate the work using a graphical tech
3、nique. If we divide the overall displacement into short segments, s, the force is nearly constant during each segment. The work done during that segment can be calculated using the previous expression. The total work for the overall displacement is the sum of the work done over each individual segme
4、nt:WF ss( )This sum can be determined graphically as the area under the plot of force vs. distance.1 These equations for work can be easily evaluated using a force sensor and a Motion Detector. In either case, the work-energy theorem relates the work done to the change in energy asW = PE + KEwhere W
5、 is the work done, DPE is the change in potential energy, and DKE the change in kinetic energy.In this experiment you will investigate the relationship between work, potential energy, and kinetic energy.OBJECTIVESDetermine the work done on an object using a force vs. distance graph. Use the Motion D
6、etector to measure velocity and calculate kinetic energy. Compare the work done on a cart to its change of mechanical energy.MATERIALSPower Macintosh or Windows PCmasses (200 g and 500 g) LabPro or Universal Lab Interface spring with a low spring constant (10 N/m) Logger Pro masking tape Vernier Mot
7、ion Detectorwire basket (to protect Motion Detector) Vernier Force Sensorrubber band dynamics cart1 If you know calculus you may recognize this sum as leading to the integral finalinitialssdssFW)(.Experiment 1818 - 2Physics with Computers PROCEDURECALIBRATE THE FORCE SENSOR1. Connect the Motion Dete
8、ctor to DIG/SONIC 2 of the LabPro or PORT 2 of the Universal Lab Interface. Connect the Vernier Force Sensor to Channel 1 of the interface, or PORT 1 if using a ULI Force Probe. If your sensor has a range switch set it to 5 or 10 N.2. Open the Experiment 18 folder from Physics with Computers. Then o
9、pen the folder that matches the type of force sensor you are using. Then open the file Exp 18a for your force sensor. Three graphs will appear on the screen: distance vs. time, force vs. time, and force vs. distance. Data will be collected for 5 s.3. If you are using the ULI Force Probe, it is neces
10、sary to calibrate the sensor. Other Force Sensors can optionally be calibrated using the same procedure, or you can skip this step. a. Choose Calibrate from the Experiment menu. Click on the PORT 1 icon (DIN 1 or CH 1 for Force Sensors other than the ULI Force Probe) so the port is highlighted. Clic
11、k . b. Remove all force from the Force Sensor. Enter a 0 (zero) in the Value 1 field. Hold the sensor vertically with the hook downward and wait for the reading shown for Input 1 to stabilize. Click Keep. This defines the zero force condition. c. Hang the 500-g mass from the Force Sensor. This appli
12、es a force of 4.9 N. Enter 4.9 in the Value 2 field, and after the reading shown for Input 1 is stable, click Keep. Click OK to close the calibration dialog. 4. Hold the Force Sensor with the hook pointing downward, but with no mass hanging from it. Click and then to set the Force Sensor to zero.Par
13、t III Work Done To Accelerate A Cart In Part III you will push on the cart with the Force Sensor, causing the cart to accelerate. The Motion Detector allows you to measure the initial and final velocities; along with the Force Sensor, you can measure the work you do on the cart to accelerate it.25.
14、Open the experiment file Exp 18c for your force sensor. Three graphs will appear on the screen: distance vs. time, force vs. time, and force vs. distance. Data will be collected for 5 seconds. If you are using a ULI Force Probe, recalibrate it as you did in Step 3. During calibration enter the secon
15、d force as a negative number to make a push on the Force Probe read as a positive value.26. Remove the spring and support. Determine the mass of the cart. Record in the data table.27. Place the cart at rest about 1.5 m from the Motion Detector, ready to roll toward the detector.28. Click . On the di
16、alog box that appears, click . Logger Pro will now use a coordinate system which is positive towards the Motion Detector with the origin at the cart.29. Prepare to gently push the cart toward the Motion Detector using the Force Sensor. Hold the Force Sensor so the force it applies to the cart is parallel to the sensitive axis of the sensor.30. Click to begin data collection. When you hear the Motion Detector begin clicking, gently
