In this experiment, a “double interrupt card” is dropped through a single light gate. The time at which each break of the infrared beam occurs is recorded. With knowledge of the width of the interrupt card, the software can determine the velocities at key stages of the fall and use these increasing values of velocity to calculate acceleration. Several trials will be conducted and an average value found.
Apparatus and materials
Light gate, interface and computer
Clamp and stand
The diagram of the apparatus
1. Assemble the apparatus as shown. 2. Connect the light gate to Input A on the datalogger. 3. Connect the datalogger to the computer and launch the Timer program. 4. Set the Timing software to record Acceleration at A in repeat mode. 5. Enter the length of the segments on the interrupt card when prompted (the segment is the solid section of the card that will pass through the light gate). 6. Begin recording and then drop the interrupt card ensuring that the light beam is broken by each section of the card.
7.Repeat the experiment many times and when enough readings have been taken, stop recording by clicking on the red square. 8.Delete any obviously obscure measurements. 9.Save your results in the recommended folder 10. Calculate the average acceleration.
How to achieve the number of the g ?
In each experiment , we measure the width of the whole card as l and the width of each interrupt part as a.
The transit time Where light beam is broken by each section of the card will be measured and we denote them as t 1 and t 2 .
From the experiment ,we can write following equations:
a=u 1 t 1 +1/2 g t 1 2 ①
a=u 2 t 2 +1/2 g t 2 2 ②
2g(h-2a)=u 2 2 -(u 1 +gt 1 ) 2 ③
In the ①, we can infer that
u 1 =(a-1/2gt 1 2 )/t 1 ④
In the ② , we can infer that u 2 =(a-1/2 gt 2 2 )/t 2 ⑤
Substitute ④,⑤ into the ③,we achieve
an equation which just has an unkown of g. By caculating , we could get the number of g.