Measuring "g" Using Video

The purpose of this lab is to measure the acceleration due to gravity of an object, otherwise know to physics-type folks as the "g lab".

A video camera is interfaced to a PC using a capture card. The camera is focused on a meter stick taped to a wall. The students then video capture the motion of a ball in free fall starting with an upward velocity in front of the meter stick. Each group makes their own video clip which is then transferred using the network to the different PC's in the lab. The video screen is calibrated for distance using video analysis software, then they analyze frame-by frame the motion of the ball as position as a function of time. Each frame represents 1/30 of a second. Data in the form of distance versus time is obtained for the dropped ball. This data is then put into a spreadsheet and the velocity and acceleration as a function of time is calculated. A graph of position versus time is made and a second order polynomial is fit to the data in order too determine g. Then a graph of the velocity as a function of time is made, a trendline is fit to this data and the slope of the line is g. Also a statistical analysis of the acceleration results is made. The students determine the mean and the standard deviation of the mean of the acceleration results. These three values of g are compared to the accepted value for the acceleration of gravity in Shreveport which has previously been determined by an advanced physics lab to be 9.795 +- 0.005 m/s2.

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