Experiment 6
INSTANTANEOUS VELOCITY

PROCEDURE


NOTE: Use the scale on the air track for Δx measurements in this experiment. All distance measurements should be made to ± 0.001 m (1 mm).

To keep the noise level in the lab down, please turn off your air supply if you are not using it.


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


I. Variation of Initial Velocity with a Level Track:

2.  Place a glider on the track, turn on the air supply and level the track with the adjustable feet at the supply end of the track. The track is level when the glider will remain nearly motionless at any point along the track. Turn off the air supply when finished.

3.  Open the Double Gate link. Make sure the interface is connected to the photogates and that it is turned on. Gate 1 is the photogate with its Signal cable connected to the DataLogger interface's DIG/SONIC 1 and Gate 2 is connected to DIG/SONIC 2. This arrangement will record the time it takes the glider to pass through each gate as Δt1 and Δt2, respectively.

4.  Place Gate 1 near the 40 cm mark or the 130 cm mark, whichever is nearer the free end of the air track (the end away from the air supply). Place Gate 2 at the other mark (40 cm or 130 cm). Adjust the photogate's height so that the glider will block it when it passes through. The message bar at the bottom of the LoggerPro window and the red light on each gate indicates when it is interrupted. Make sure the gates are perpendicular to the track.

5.  Turn on the air supply. Give the glider a gentle push from the free end of the air track. Catch it at the supply end. When the program stops, click on the Table Window. The times for the glider to pass through Gate 1, Δt1, and Gate 2, Δt2, are shown in the Table Window.

6.  Repeat the procedure for a total of five different initial velocities. The time for the glider to pass each gate will be recorded as a column of data in the Table Window.

7.  Use the mouse to select the data for all 5 runs in the Table window. Under the EDIT menu, select COPY. Switch to the Worksheet window and select cell D10. Under the EDIT menu, select PASTE to transfer the data.

8.  Switch to the LoggerPro application and close it by choosing FILE...QUIT---Don't Save.


II. Mid-distance Interval Velocity/ Inclined Track:

9.  Open the Gate-to-Gate link.

a.  Place the photogates so they are 60 cm on each side of the 100 cm mark, i.e. at 40 cm and at 160 cm. Block up the free end with the thin plywood shim so that a glider that starts from rest at the free end takes between 2 to 4 sec to move from Gate 1 to Gate 2, read as Δt1 in the Table Window.

b.  Turn the air supply off. Carefully measure and place the glider so that the front of it is 60.00 cm from the 100 cm mark. You can do that with an uncertainty of about 0.5 mm. Adjust the position of the nearest photogate so that the glider just trips the beam. This is easily done by sliding the photogate toward the front of the stationary glider until the indicator on the lower data bar just starts to show that the gate is blocked. Now repeat so that the other photogate is tripped at the other mark.

c.  Let the glider start from rest at the free end of the air track (do not push it) and record the time for the glider to move the 120.0 cm (Δx) between the gates. Repeat so that you have five time measurements of Δt1 to average. COPY and PASTE the five measurements from the Table Window to the Worksheet in cells B20:B24.

10.  Repeat procedures 9b and 9c for Δx = 100.0, 80.0, 60.0, 50.0, 40.0 cm. In each case, keep the 100 cm mark midway between the photogates. Make sure that you start the glider from rest at the free end each time. You should now have the Worksheet table completed.

11.  Use the spreadsheet calculator function to compute the average Δt for each column in cells B25:G25.


III. Mid-time Interval Velocity/ Inclined Track:

12. 

a.  Using same procedure as in step 9b, place Gate 1 on the "up-hill" side 40.0 cm from the 100 cm mark. Adjust the position of Gate 2 so that the glider trips the beam when the front of the glider is at the 100 cm mark.

b.  Take five readings of the time for the glider to move between the photogates. Start the glider from rest at the free end of the track each time. Copy and Paste the data in cells B30:B34.

c.  Using the spreadsheet calculator, determine the average Δt1 from these 5 runs, and enter the result in cell B35. In cell F31, enter twice this value.

d.  By trial and error, find the position for Gate 2 that gives a travel time for the glider between gates which is twice the average time. This position makes the 100 cm mark be at the mid-point of the Δt interval.

e.  Carefully determine the distance Δx between the points where each photogate is blocked by the glider. You will want to have the air supply off as you measure Δx. Enter the result in cell F33.