ANALYSIS OF A KIND OF SYSTEMATICAL ERROR ABOUT USING PHOTOELECTRIC GATES TO MEASURE VELOCITIES IN THE EXPERIMENT OF VERIFYING NEWTON'S SECOND LAW

This paper derives the accurate velocity of the center of the shading strip passing through two photoelectric gates in the experiment to verify Newton's second law, and the strict result of the slider's acceleration is also deduced. The analysis shows that these strictly accurate results are almost indistinguishable in magnitude from the measurement results obtained in common experiments where average velocity is used instead of instantaneous velocity, that is, the systematic error brought by the usual practice in experiments is almost zero. However, in terms of qualitative nature, the measured velocity is slightly less than its accurate value, while the measured acceleration is slightly greater than its accurate value. To enrich the content, this paper further infers the relative error of the measured acceleration expressed by the width of the light-blocking strip and its two segments of displacement, and judges the trend of the relative error with the changes of various parameters based on this. Although this paper is essentially a theoretical study and has little reference value for actual experiments, its theoretical reference value objectively exists, and it should be of some help for the teaching of related content in universities and middle schools as well as the cultivation of scientific literacy.