PHYS 1405: Acceleration on Air Track
Equipment:Air Track, Car & Flag, Lab Jack, Computer running Vernier Logger Pro
Objective: To gain conceptual understanding of acceleration through experimentation and analysis of a car floating on an air-track. To learn how to calculate the acceleration of the car from velocity and time data.
Introduction:Acceleration, “a”, is the rate of change of velocity in units of (m/s)/s. If the velocity of an object remains unchanged, we say it has an acceleration of zero. If the velocity of an object changes in any way, then it has a non-zero acceleration. We will determine a car’s acceleration by measuring the change in its velocity during a known time interval.
1. Level Track.
1)Turn on the air to 2/3 full power. Adjust the level screws on the two-footed support at the bottom of the air track until a car at the center of the track is nearly motionless.
2)Set two photogates 40cm apart near the center of the track. Adjust their height until only the flag on the car blocks the light beam. Verify the 40cm distance by measuring with a meter stick.
3)Connect the photogates to the “DigSonic” 1 & 2 slots in the data logger. Plug in the data logger and connect it to a USB port on the computer.
4)Start the computer and then open the Logger Pro program. Click “open” folder and follow the path to open: Probes & Sensors/Photogates/Two Gate Timing.
5)Read the instructions at the bottom left of the program and change the flag length of the program if its preset length is different from the flag you are using.
6)Click the green “Collect” button at the top of the program. Launch the car so that it will pass through Gate 1 first and then through Gate 2. Do not allow the car to go back through the gates. Carry the car around the gates and repeat four more times, varying the launch speed somewhat. Do not attempt very high speeds. If the car falls to the floor it can never be used again.
7)Does the calculated acceleration of the car appear to be affected by the launch speed? ____ Note that the only factor that should affect the car’s acceleration is the track’s inclination angle.
Table 1: Level Air Track data taken with varying launch speeds.
Trial / Velocity 1 (m/s) / Velocity 2 (m/s) / Elapsed Time*(s) / Acceleration =
{Vel.2 – Vel.1}/(Elapsed Time)*
(m/s/s)
1
2
3
4
5
*Elapsed Time is the time-difference between the left side “Time (s)” on the program window from the same rows that contain “Velocity 1” and “Velocity 2” data. It should be a positive quantity.
2. Inclined Track. Car moving down the incline.
1)Carefully prop up the one-foot end of the track with the lab jack. Ensure that Gate 1 is on the high end of the track. If it is not, exchange the plugs from the gates so that it is.
2)Set two photogates 10cm apart near the center of the track. Adjust their height until only the flag on the car blocks the light beam. Verify the 10cm distance by measuring with a meter stick.
3)Click the green “Collect” button at the top of the program. Release the car from rest so that it will pass through Gate 1 first and then through Gate 2. Catch the car at the bottom. Do not allow the car to go back through the gates. Record the two velocities in Table 2: Trial 1.
4)Set two photogates 20cm apart near the center of the track. Adjust their height until only the flag on the car blocks the light beam. Verify the 20cm distance by measuring with a meter stick. Release the car from rest above the top photogate. Record the two velocities in Table 2: Trial 2.
5)Repeat Step (4) for 30cm and 40cm separation distances, recording the data in Table 2.
6)Calculate the acceleration of the car for each trial and record in Table 2.
7)Does the calculated acceleration of the car appear to be affected by the gate separation distance? ____ Note that the only factor that should affect the car’s acceleration is the track’s inclination angle.
Table 2: Car moving down the track.Varying gate separation distances.
Trial / Velocity 1 (m/s) / Velocity 2 (m/s) / Elapsed Time*(s) / Acceleration
(m/s/s)
1
2
3
4
Table 3: Car moving up the track.
Trial / Velocity 1 (m/s) / Velocity 2 (m/s) / Elapsed Time*(s) / Acceleration
(m/s/s)
1
2
3
3. Inclined Track. Car moves up the track.
1)Keep the track inclined with lab jack. Ensure that Gate 1 is lower in elevation than Gate 2. If it is not, exchange the plugs from the gates so that it is.
2)Click the green “Collect” button at the top of the program. Lauch the car from lower end of the track so that it will pass through Gate 1 first and then through Gate 2. Do not allow the car to go back through the gates. If you have trouble getting the car to go through both gates try putting the gates closer together.
3)Repeat two more times, varying the launch speed somewhat. Do not attempt very high speeds. If the car falls to the floor it can never be used again.
4)Calculate the acceleration of the car for each trial, recording the data in Table 3.
5)Are the acceleration values in Table 3 similar to those in Table 2 in any way? ____. (Remember that negative signs express opposite directions.)
1