Experiment 9
WORK AND ENERGY

PROCEDURE


The apparatus consists of the linear air track used in previous experiments and two photogates to measure the speed of a glider at two fixed points on the track. A photogate is a photocell and light source connected to an electronic timer in such a way that whenever the light hitting the photocell is interrupted, the timer is turned on. The timer is turned off as soon as the light again hits the photocell. Two such photogates are placed across the air track at two points A and B. The light hitting the photocell is interrupted by the glider. As the glider passes through each gate, the transit time is measured. From these measurements the speeds of the glider at points A and B are calculated.

1.  Open the Worksheet and fill in the header information.

2.  In this experiment, it will be necessary to make two successive measurements of the time interval required for a glider to pass through a photogate.The two photogates should have their signal cables connected to DIG/SONIC 1 and DIG/SONIC 2 of the DataLogger interface. Turn on the interface with the switch, and open the Two-Gate Timer link.

3.  Set up a photogate at two points, A and B, at about 30 cm from each end of the track.

NOTE: Positions A and B are equivalent to inputs 1 and 2 of the DataLogger interface as indicated in Figure 9-3.

4.  Make sure that gate #1 (the one connected to DIG/SONIC 1) is at the higher position, point A. Hit Collect in the LoggerPro window to begin taking data.

5.  Level the track and test the arrangement of the photogates by launching the glider on the leveled track. The transit times ΔtA and ΔtB should be equal to within a few milliseconds or so. When everything checks out, elevate one end of the track 3 to 5 cm by placing a shim under the single-foot end of the air track.

6.  Measure and record the length L of the glider and the distance d between the photogates each to within 1 mm. Record these data on the Worksheet in cells F9 and F11, respectively.

7.  A series of measurements consists of ten measurements (runs) of the transit times of the glider through gates A and B. Five of the runs should be for motion down the incline, and five of the runs should be for motion up the incline. For each measurement, try to launch the glider with a different initial speed. Record values of ΔtA and ΔtB on the Worksheet for each run. For motion down the incline, fill cells D14:E18, and for motion up the incline fill cells D22:E26.

8.  Finally, measure and record the thickness H, of the shim placed under the track in cell F29. Record the baseline distance D between the legs of the track in cell F31, and the mass M of the glider in cell F33.