Day 10: Experiment and PASCO Troubleshooting

Today, the team continued analyzing the videos from the previous day to determine if the various positions of pitch and tilt on the camera affected the data which can ultimately cause an error in the g value. The videos from the previous day, as mentioned in the last post, contained videos shot with a 20 and 30 degree tilt on the phone as well as a front and backwards pitch of the phone separately (the apparatus and procedure is shown much clearer in the previous post.)

The acceleration due to gravity from videos with front and backwards pitch had a noticeable trend of a decreased value of g. This trend may be due to the fact that the camera was pitched front or backwards causing a distorted view of the meter stick -which acts as our scale in the video; having an inaccurate scale will subsequently cause inaccuracy in data. Therefore, it is imperative to have zero pitch to get the most accurate results.

Next, the team analyzed videos shot from a 20 and 30 degree angle and discovered a massively important issue which may be one of the primary cause of error for past trials and for future (if not taken into consideration.) This being: a sideways tilt, as seen in figure 1 below, will cause the distance of vertical travel in PASCO to be shorter than intended.

Figure 1. Camera Side Tilt

This error can better be shown in figure 2 and 3 below. As seen in figure 2, the yellow x and y axis was left at the initial position, which is square with the sides of the video itself. The problem with this is that the travel of the ball, shown as the red crosses, is perceived as both x and y travel in PASCO since the axis has not been adjusted . In actuality, the ball travels in a perfect vertical line from the starting position to ending position (assuming air resistance does not affect the ball.) However, PASCO will only interpret the vertical component of the ball's travel  in the video since that is what the program perceives as the true vertical axis -because the program abides by the yellow x and y axis- and not the travel shown from the red crosses. In short, to find the most accurate value of g using PASCO, the user must manually adjust the yellow x and y axis to have the y axis parallel with the ball's actually travel. This will nullify any effect of a sideways tilt of the phone, thus eliminating a large possible error. As seen in figure 3, the value of g is now closer to the intended value. To adjust, you must click on the yellow dot on the x axis and y axis to tilt and move around.

Figure 2. Unadjusted Axis

Figure 3. Corrected x and y Axis

The team also experimented with using the auto track feature in PASCO, but the data found is not reliable since the program sometimes misinterprets the position of the ball. Therefore, it is recommended that users should manually track the position of the ball in order to get accurate results.