Blog of First Lab Zitong Cheng

 Acceleration from Motion Detector
1. I measure the volocity of the ball, and also the displacement of the ball more in that period by motion detector.

2.We set up the lab equipments and connected to the computer, open the Logger Pro, and start our lab. Place the Motion detector 1.5 meters away and hold the ball 20cm away from the motion detector. hold it still. When we start recording data, we release the ball, after it hits the ground, we stop collecting data, and analyze the data by Logger Pro.

Measuring the velocity of the ball by motion detector, and divided the speed into veritcal speed and horizontal speed. Using Logger Pro to analyze the graphs, clik the analysis bottom and choose linear fit and quadratic fit to spearately analyze the graph to get the equations. Then we can get the frist acceleration from the equation of horizontal speed vs time graph, and get the another acceleration from the equation of vertical postion vs time graph by take derivative of the equation twice.

3. The result(acceleration) is -9.65 m/s^2(horizontal speed vs time graph) and -9.6 m/s^2( vertical postion vs time graph)

4. By adding other groups data and calculates, we can get the standard deviation= 0.183 m/s^2

Acceleration from vedio analysis

1. We measure velocity, position and time to get the accelerations.

2. I first recorded a video of throwing the ball in front of me. In this video, I kept still and threw the ball, with a two-meter ruler directly in front of me, until the ball hit the ground and stopped recording the video. Then upload the video to the video analysis software, adjust the scale to 2 meters, make the scale coincide with the ruler, adjust the time to the moment when the ball just left the hand, then click the ball repeatedly to record the position of the ball at different times until the ball hits the ground, adjust the coordinate axis so that the position when the ball just left the hand is (0,0). Gets different graphs.

3. Geting the equation of the graphs, and take derivative of the equation to get the acceleration, which is -9.6 m/s^2.

4. The standard deviation is equals to 0.223 m/s^2

Write-up on measurement variability

1. % difference=3.4%

2.  My measurement agree within the uncertainty determined from the standard deviation because 0.406 is bigger than 0.3202.

3. The measurement have uncertainty when using motion detector are: （a)The distance between the ball and the ground is not exactly 1.3m. (b) Motion detecor Inaccurate displacement measurement caused by not being parallel to the ground.

4. The measurement have uncertainty when using vedio analysis are: (a)We can't take the same point of the ball every time. (b)You can't be particularly accurate when adjusting the scale. (c)Error in measuring the horizontal displacement of the ball caused by the camera not being parallel to the ball's motion trajectory when recording video.

5.The data for motion detector: -9.5172 +/- 0.183 m/s^2 .

   The data for vedio analysis : -9.197 +/- 0.223 m/s^2 .
                    

6. I get -18.7142 +/- 0.406 m/s^2 for my uncertainty, using addition method.

7. I think the data for my motion detector is more reasonable, because the uncertainty of motion detector is smaller than the uncertainty of vedio analysis which means the data of motion detector is more accurate, therefore, the method of using motion detector is more useful.