Gravitational Acceleration Golf Ball Lab
Adam Seering
In this lab, using a strobe light, a digital camera, and a golf ball, we determined the acceleration due to gravity. The digital camera was used to take a long-exposure picture of the golf ball falling with the strobe illuminating it every 1/15 of a second. The resulting picture was analyzed, and by measuring and graphing how far the ball traveled between each blink of the strobe, the acceleration due to gravity was calculated.
For the first step in this lab, we used a digital camera, a strobe light, and a golf ball. We set the frequency of the strobe to 900 (this display probably indicated blinks per minute, although this information was not provided; we were just told that this number represented a blink every 1/15 of a second), and set the camera to take a picture over several seconds. We then aimed the camera at a black wall with a meter stick taped to it (used as a scale for the photograph), and took a picture of the golf ball dropping along the wall with the strobe light flashing on it. The resulting picture showed the golf ball's precise position every 1/15 of a second:
The next step was to measure and graph the data in the photograph. We measured how far the golf ball had traveled from its starting point in each 1/15-second interval, and created a distance vs. time graph (see graph below). We then calculated the average velocity of the ball between each of the data points by dividing the displacement by the time, 1/15-second, between each interval. This data was plotted as well, and a best-fit line for it was drawn (see graph below); the data appeared to be roughly linear, so this was feasible.
The line represented velocity vs. time, so its slope represented acceleration vs. time. We selected two sample points on the line and measured the rise and run between them, and used this information to calculate the slope (slope = rise/run). The result of this calculation was {Acceleration = 9.75 m/s2}. This information was graphed as well (see graph below).
This lab concluded that the acceleration due to gravity is very similar to the previous approximation that we had been given, 9.80 m/s2. It is, in fact, the same to two significant digits, which was near the accuracy of our measurements. Air resistance could account for a significant part of that difference; it was disregarded entirely for our calculations, but it is known to slow falling objects. The system of taking measurements of the golf ball's position also had many potential faults. Firstly, the digital picture was processed through several pieces of software and hardware before we could measure it; any one of these could have introduced some error. Secondly, it's hard to measure the precise location of a circle on a flat sheet of paper; we measured to three significant figures, but we could really only get two with any accuracy. None of these are major sources of error, though; even given them, this experiment effectively demonstrated that "gravity" is a constant acceleration of about 9.8 m/s2.