Experiment of The Month

VideoPoint software makes it easy to observe both the terminal velocity of a falling object and the approach to terminal velocity. The object is this case is a pair of coffee filters, mashed with a fist into approximately the shape of a rocket nose cone, as in our first experiment of the month. The coffee filters are dropped from a height of about 2 meters. Students at each lab bench record the fall with a digital video camera and the data are stored on their computer.

The figures show (on the left) one frame of the video record of the falling coffee filters, and (on the right) the VideoPoint trail of positions for each of the video frames during the fall

With the VideoPoint software students record the position of the falling filter pair, for each frame of the video record. The position and time data are transferred to an Excel spreadsheet, and used to calculate the velocity as a function of fall time. The resulting graphs are shown below.

In this case, the filter was dropped about 3.5 seconds after the video recording was begun. The data were taken January 25, 2005, by Physics 231 students David Crotsley, Jeffrey Moser, and Craig Smoker.

The position graph shows the filter starting slowly (with a low magnitude of slope) and speeding up. Its graph becomes a straight line, until the last two points, which indicate the filter is sitting still on the floor.

The velocity graph shows the velocity increasing in a downward direction until about 4 seconds into the video record. At that point the calculated velocity is noisy, but essentially constant, until it falls to zero at the last point.