Application of air track

1. Application of air track School of Electronic & Applied Physics, Hefei University of Technology

2. The objective of experiment • 1. Understand the basic structure and the principleof air track • 2. Master the adjustment and operation method of air track • 3. Measure the slider’s velocity and acceleration on air track

3. Laboratory Instruments • 1.Air Track Shown in the figure 1: there is an air layer between the slider and the track, the friction is so small that it can be neglected, when the slide is moving on the track

4. Laboratory Instruments • 2.Optical measuring system (1) Shading flake (shown in figure 2) (2) Optical gate (shown in figure 3) is composed by infrared LED and photodiode. it can control the timer to record time because it can generate the difference electrical signals when the photodiode is shaded or is not shaded.

5. Laboratory Instruments (3) Digital timer CS-Z digital timer can record interval between the two times the photoelectric gate is shaded. When the shading flake A side goes through the photoelectric gate, digital timer begin to record, when the shading flake B side goes through the photoelectric gate, digital timer stop recording. Therefore, the time recorded by digital timer is the time that shading flake goes in distance of dx. Then the velocity of shading flake is v=dx/t. digital timer

6. Experimental principle • 1. Speed Measurement：v=dx/t • 2. Verify Newton's Second Law (1) Acceleration measurement: shown in figure 4

7. Experimental principle (2) When systemic quality keeps unchangeable, the systemic acceleration is proportional to external force applied on system. • Select six weights that have the same quality, at first put four weights on the slide, then put two weights at the other end of the tape. At this time the external force of the system is F = 2mg, The quality of System is M=Mo+6m • Second, put two weights on the slider, put four weights on the other end of the tape. At this time the external force of the system is F = 4mg, The quality of System is M=Mo+6m, Therefore, External force increased as the quality unchanged. • Third, put six weights in the other end of the tape, at this time the external force of the system is F = 6mg, The quality of System is M=Mo+6m. Therefore, External force still increased as the quality unchanged. • Verification: 2mg/a1=4mg/a2=6mg/a3=Mo+6m

8. Experimental principle (3) When external force keeps unchangeable, the systemic acceleration is inversely to systemic quality. • Put the six same weights on the other end of the tape. • First, select the big slide, at this time the external force of the system is F=6mg，The quality of System is M=Mo+6m • Second, select the small one, at this time the external force of the system is F=6mg，The quality of system is M=M’+6m,Therefore, external force has not changed, but the quality has changed. • Verification:a1（Mo+6m）=a2（M’+6m）

9. Experimental principle (4) Measure the acceleration for slide slip down along the ramp free. • Booster one end of the air track to form a ramp ,put the big slide on the top of ramp ,then let it free fall. • Verification: a=gsin =gh/L L is the length of track, H is the height pad.

10. Content and procedures of experiment: • 1. Level the Air track (1) Coarse adjustment: put the big slide on the middle of track, regulation under the direction of slide movement (2) Fine adjustment: Digital timer options 1pr, Auto Reset, let the slide move on the track back and forth, observe: t4-t3 and t2-t1, if they are both greater than zero and generally equal, the track is in balance.

11. Content and procedures of experiment: • 2. To measure the speed • 3. Verify Newton's Second Law • 4. Measure the acceleration of objects gliding along the ramp All the process repeated three times

12. The difficulty and solution of teaching • 1. Adjusting the air track is difficult for students. We should pay attention to clarify the regulation of the principle and the method of adjustment. • 2. Students should be taught to check their own experimental data. As the contents of each must be repeated three times, you can ask students to repeat it in the same conditions so that the three sets of data would be basically the same.